Evidence - Admissibility - Opinion evidence - Expert opinion - Particular cases - Fire investigation expert - No evidence of truth of some information relied on by witness.

Evidence Act 2001 (Tas), ss 60, 79, 135, 136, 137.

Dasreef Pty Ltd v Hawchar [2011] HCA 21, 243 CLR 588; Taub v The Queen [2017] NSWCCA 198, followed.

Judgment Number: [2018] TASCCA 1

1. I agree that this appeal should be dismissed, for the reasons stated by Brett J.

1. On 24 August 2017, the appellant was found guilty by a jury of one count of unlawfully setting fire to property. It was alleged at the trial that the appellant, a taxi driver, had set fire to a taxi owned by another driver in the early hours of the morning of 23 February 2016. The taxi, a Toyota Prius, had been parked for some hours beside an automotive building at a service station at West Launceston. The case against the appellant was circumstantial. Important pieces of circumstantial evidence were CCTV footage which showed the appellant walking away from the vehicle at the time that the fire commenced, and the opinion of the fire investigator that the fire had started on the external surface of the car, in particular the rear bumper bar. This opinion, if accepted, excluded the possibility that the fire may have commenced accidentally as a result of a malfunction of equipment within the vehicle, for example, the battery or electrical circuitry.
2. The fire investigator based his opinion on a number of pieces of information. The majority of this information came from his observations and examination of the scene. He interpreted this information, and formulated his opinion, having regard to his specialised knowledge as to the cause and behaviour of fires. This knowledge had been acquired from his experience and training in that field. The methodology of the formation of his ultimate opinion consisted of the preliminary identification of possible sources of the fire, followed by the elimination of as many as possible on the basis of more detailed investigation. One of the possible causes of the fire, identified in the preliminary stage of the investigation, was an electrical fault within the vehicle. However, the investigator did not have expertise in the electrical circuitry of motor vehicles generally, including a Toyota Prius, which is a hybrid vehicle. Accordingly, he consulted an unnamed person or persons at the Toyota dealership in Launceston. The person or persons he spoke to said that they were not aware of problems with the electrical circuitry of that model. He was also told that use of an incorrect battery could be a fire risk. He took the battery from the taxi to Toyota and confirmed that it was the correct type for the vehicle. He then carried out a further inspection of the vehicle, looking for evidence that the fire had commenced internally. He did not locate any such evidence. Ultimately, he formed the opinion that the fire had not been caused by an electrical fault. The person or persons from Toyota who provided the information were not called to give evidence. There was a degree of imprecision in the evidence of the investigator as to the role that this information played in the formation of his ultimate opinion, and, in particular, his exclusion of electrical fault as a cause of the fire.
3. At trial, the defence objected to the fire investigator giving evidence of his opinion as to the fire starting on the external surface of the vehicle on the basis that his opinion depended on the exclusion of electrical fault as a cause, that he did not have the relevant expertise to assess or form an opinion about that question, and that any opinion he expressed was, in reality, the opinion of an unidentified person at Toyota, who would not give evidence. The trial judge, Pearce J, conducted a voir dire and then ruled that the evidence was admissible, although he directed the jury that the evidence of what the fire investigator was told by Toyota was not admissible to prove the truth of those representations, and this may affect the weight that they should attribute to the opinion.
4. The appellant appeals against his conviction on the basis that the trial judge erred by admitting the opinion evidence of the fire investigator. The grounds of appeal raise the following issues:

(a) Whether the evidence was excluded by the opinion rule (the Evidence Act 2001 (the Act), s76), and not excepted from that rule on the basis of the witness's specialised knowledge under s 79.

(b) In any event, whether without proof of the facts asserted by the out of court representations of the persons at Toyota, the opinion was so lacking in probative value that it ought to have been excluded under ss 135 and/or 137 of the Act.

1. The appeal squarely raises the question of whether proof of the facts and assumptions upon which expert opinion is based is a necessary precondition of admissibility under s 79 of the Act and, if not, the consequences of lack of such proof on the probative value of the opinion.

1. The unchallenged evidence presented by the prosecution established that the taxi had been parked in an outdoor wash bay at the side of the automotive building from about 8pm on 22 February 2016. The driver had left the vehicle there for the night. The vehicle was left locked, with the windows closed.
2. Shortly before 2am, another taxi driver, who had come to the automotive building to park his taxi after a shift of work, found the Toyota Prius on fire. The fire was well established. From the front of the vehicle, he observed flames dropping underneath the vehicle as if plastic was melting and dripping to the ground. The driver immediately rang 000. There is evidence that the fire brigade was alerted to the fire at 2.03am.
3. It was established on the basis of booking records from the relevant taxi company, and confirmed by the appellant in his evidence, that he was undertaking a journey for a passenger in the area shortly before the fire was discovered. CCTV footage which displayed an area immediately adjacent to the location of the Prius, but not the vehicle itself, shows the appellant walking in the direction of the vehicle at 1.46am. At 1.49am the appellant can be seen walking away from the vehicle. At one point he looks back towards the vehicle and shortly after smoke can be seen emanating from the direction of the location of the vehicle.
4. In his evidence, the appellant agreed that he was the person shown in the CCTV footage. He said that he had been driving his taxi in the area and had gone to the wash bay because he needed to urinate and thought he could do so unobserved in the wash bay behind cars. He denied that he had set fire to the vehicle. In cross-examination, he said that he could not remember looking back at the vehicle as he walked away. He claimed that he saw three youths sitting in the gutter nearby, although they did not "appear to be causing any trouble".
5. The appellant agreed that he had gone back to that location at about 3am and had spoken to the owner of the premises at that time. He said that he was driving past, had seen the fire brigade and had decided to investigate.

1. The impugned evidence is that of Station Officer Paul Catterall. Mr Catterall's evidence before the jury was that he has been a fire fighter for 25 years, and has received a number of promotions to reach his current rank. He has undertaken formal training in fire investigation, together with ongoing training in the form of study, attendance at courses and peer review. He estimated that he had attended around 2,400 fires during his time as a fire fighter, which included approximately 350 vehicle fires. This evidence was relevant to the prosecution's claim that Mr Catterall had specialised knowledge in the cause and behaviour of fire, based on his training, study and experience.
2. Mr Catterall testified that he and other fire fighters had responded to the 000 call. They arrived at the fire at about 2.13am and extinguished it. He then immediately commenced an investigation with a view to determining the most probable cause of the fire.
3. Mr Catterall described his investigative methodology as follows:

"Yes the science and theology [sic] about the fire investigation is to identify hopefully a point of origin but you would like to at least identify an area of origin or a radius of origin. Then you use the timeline of events, what people tell you, and fire language which there are three main contributing factors. Then you identify the possible ignition sources in that area and you go through a process of eliminating those ignition sources that you've identified - identified until you come up with the most probable cause for that fire."

1. Mr Catterall expressed the ultimate opinion that the fire had commenced low down in the rear external surface of the vehicle. This opinion was based on the following:
   • The fire language indicators demonstrated that the lowest point of burning was outside the vehicle on the rear bumper. In particular, a V pattern demonstrated that the fire had developed on the rear bumper, moved over the top of the vehicle and caused the rear window to break, hence enabling flames to enter the vehicle. An internal V pattern showed that flames had moved from the rear of the inside of the vehicle.
   • The fire language indicators were supported by information from the taxi driver who had located the vehicle. He had told Mr Catterall that he had seen "the fire burning outside and plastic melting on the ground". As already noted, this information was confirmed by the taxi driver's testimony.
   • There was an absence of discolouration of the internal glass of the front and passenger side windows. According to Mr Catterall, this indicated an absence of soot residue. Such residue would be expected if the fire had commenced internally, for example as a result of an electrical fault, because having regard to the evidence which indicated that the windows were closed, the fire would be expected to firstly create dense black smoke which would cause soot residue on the inside of the windows and then to self-extinguish from lack of oxygen. The absence of such residue was therefore consistent with the fire commencing externally and then moving into the interior of the vehicle through the broken rear window.
2. Mr Catterall also took steps to exclude the possibility that the fire had commenced spontaneously as a result of a fault in the electrical circuitry. He indicated that he had "some apprehension in relation to the electrical componentry". He explained, in particular, that the vehicle in question was a hybrid and he was not familiar with the electrical componentry of that type of vehicle. He was concerned about an enhanced fire risk. He therefore contacted "someone at Launceston Toyota", raised the question of the electrical circuitry and wiring of a hybrid vehicle in the context of fire risk, and was told that "there had been no issues in the past in relation to either the battery or the circuitry as far as they were aware". He was also told that there could be a problem if an incorrect battery was in the vehicle. He then retrieved the battery from the vehicle and took it "back to Launceston Toyota on the basis that we wanted to ensure it was the correct battery". He was informed, again by an unidentified source, that it was the correct battery.
3. Mr Catterall then personally checked aspects of the electrical circuitry. This included the fuses, checking to see if the battery terminals were connected, and looking for signs of electrical arcing or beading. He was looking for marks or discolouration which would be consistent with the fire having been caused by shorting in the electrical circuitry. He also conducted an examination of the battery and its connections to the electrical system. He found nothing that was consistent with the fire having commenced in the battery or the electrical circuitry.
4. In cross-examination, defence counsel put to Mr Catterall directly that it was possible that the fire had been started by an electrical fault within the vehicle. He conceded the possibility but also said:

"Um, through the investigation process and with the information that we gathered, and the information that we sought, it's most probable that the fire started from the - indicate as a fire, the timeline, the people that we spoke to, it's - it's most probable that it started externally."

1. In re-examination when asked how likely it was that the fire started through an electrical fault, he said:

"Um, very unlikely from the information that we received and the indicators of fire and fire language and the timeline and people that we spoke to."

1. As a result of defence counsel raising an objection to the proposed evidence of Mr Catterall, his evidence to the jury was preceded by a voir dire. The only witness called on the voir dire was Mr Catterall.
2. The evidence of Mr Catterall on the voir dire was largely reflected in his evidence at trial, as summarised above. However, in cross-examination, he was pressed in considerably more detail and length than at trial, concerning the significance of the information provided by Toyota and its impact on his opinion. In particular, defence counsel questioned him about a passage in his report that noted that before consulting Toyota, he had formed "an initial conclusion" that a fault in the electrical system of vehicle was "a probable cause of the fire". Mr Catterall agreed that the battery was located in the rear of vehicle and that the fire language was consistent with the fire having commenced towards the rear of the vehicle. He agreed that his initial findings indicated "a possibility that it had been the battery". However, he consistently asserted that irrespective of the manner in which his report had been worded, he had ultimately excluded the battery as the cause of the fire and had determined that the fire had commenced on the external surface of the vehicle, in particular the rear bumper. He agreed that he had, after his preliminary investigation, sought advice from Toyota and was told that they were not aware of problems with the electrical componentry. They had also confirmed that the battery was the correct type for the vehicle. He was adamant that he was able to exclude the battery and electrical fault generally, irrespective of this information, having regard to his own observations and investigations. The following exchange was typical of this evidence:

"Now do you accept you sought the expert advice about the electrical system of Toyota - from the Toyota people of the Toyota Prius?.....Yes.

And you accept you sought their expert advice into the battery as well?.....Yes.

Okay. And it was based upon that advice that you reached your conclusion in respect of the auto-electrical and battery situation being potential causes of the fire?.....Again, along with the other indicators of fire and the other, other information and investigation that we-

The only, the only other information that you sourced after that occasion was viewing the CCTV footage?.....No. On our second investigation of the vehicle, we, we again looked at the V patterns and the language of fire in association with the spread from the rear and, for instance, the sooting on the glass."

1. A reasonable summary of the effect of this evidence is that, consistent with the methodology described above, the battery was identified at an early stage in the investigation as a potential ignition source. After the consultation with Toyota, Mr Catterall conducted a number of further investigations and made observations himself. On the basis of all of this information, he excluded the battery as a cause of the fire. It is a reasonable assessment of this evidence that the only role played by the information obtained from Toyota was the identification of the battery as the correct battery for the vehicle. This was a piece of factual information which was not otherwise within the knowledge of Mr Catterall. It clearly played some role in the formation of his opinion, although the extent of that role was not clear.

1. At the conclusion of the voir dire, defence counsel stated the nature of the objection during the course of submissions. Counsel argued that the evidence established that Mr Catterall's preliminary view was that the battery could have caused the fire, and that nothing had changed after the formation of that opinion, except for the consultation with Toyota. Although after that consultation, he looked again at the objective evidence and excluded the battery as a cause, all of that objective evidence was available to him when he formed his preliminary view. Hence, counsel argued, any change or modification of his preliminary opinion must have come about because of his discussions with Toyota. To that extent, his opinion was not based on his own observations and specialised knowledge but simply transposed what Toyota had told him. Even if this was not the case, the Toyota information must have had some effect, and the lack of precision and clarity about the extent of that effect made the use of that evidence unfair. Hence, it should be excluded under ss 135 and 137 of the Act.
2. With respect to counsel, the submissions did not accurately portray the substance of Mr Catterall's evidence on the voir dire. As already noted, Mr Catterall flatly rejected the suggestion that his subsequent investigations and observations had not been relevant to the formation of his opinion. In fact, his evidence on the voir dire was that he would have arrived at the conclusion which excluded the battery and the internal commencement of the fire, irrespective of the information from Toyota. Notwithstanding this, there was some merit in the submission that there was a degree of imprecision around the actual effect of the Toyota information on the formation of his opinion.

1. His Honour ruled that the evidence was admissible. In his ruling, the trial judge noted that Mr Catterall maintained that he had formed his opinion independently of what he had been told by anyone at Toyota. His Honour, however, determined that "it is open to the jury to conclude that what he was told played some part, in combination with other evidence, ... in the formation of his ultimate opinion".
2. His Honour went on to say:

"In my view the evidence to which I have referred should be admitted. It is not adduced as evidence of the truth of the representations made to him, see section 59, moreover by section 60 of the Evidence Act the hearsay rule does not apply because the evidence is relevant for a non-hearsay purpose, that is, as evidence of the basis of an expert's opinion.

Counsel for the accused submits that the evidence of the statements made to Mr Catterall gives rise to unfair prejudice. In my view that concern is appropriately dealt with by limiting the use which can be made of the evidence under section 136 so that it cannot be used by the jury as evidence of its truth and by directing the jury about the dangers of hearsay representations, in particular the absence of evidence of the truth of the representations and the inability to test or challenge the assumptions apparently made by Mr Catterall.

Beyond that the issue goes only to the weight of Mr Catterall's opinion. He can be cross-examined about the extent to which what he was told influenced his ultimate opinion and I will give the usual directions about the use the jury may make about expert opinion evidence."

1. The trial judge dealt at some length with Mr Caterrall's evidence in his summing-up. He discussed Mr Catterall's opinion that the fire had started externally near the rear bumper but pointed out the defence argument that Mr Catterall, when he had first inspected the car, had formed the opinion "that a possible or even probable cause of the fire was an electrical fault but he later altered that opinion after receiving further information". The information was from an employee of Toyota. He had been told that there were no issues with the battery or circuitry in hybrid vehicles in the past, to Toyota's knowledge. His Honour went on to say:

"... it seems to me to be inescapable that one of the factors which Mr Catterall used to form his ultimate opinion, was what he was told by the Toyota man. It wasn't the only thing. He gave you evidence about the examination of the car and so forth, but, I would point out to you that the evidence of what he was told, does not make it true and you may not use evidence of what he was told as evidence of the truth of what he was told. You've not heard any other evidence from any person, expert or otherwise, about the electrical systems of a Toyota Prius or whether batteries or any other alterations to a Prius to fit it out with a taxi, may cause a fire and there are a number of effects of that. The first is, that the accused, through his counsel, is at a disadvantage because he can't test or challenge the correctness of the assumptions Mr Catterall used to form his final opinion. Mr Catterall says he was told something. You can't assume that what he was told was true and not only that, Mr Langford can't test or challenge whether it was true. Further, you've not been able to form your own view about the correctness or reliability of what Mr Catterall was told about cars of this type."

1. His Honour then went on to deal with the question of whether the battery in the vehicle was the correct battery. He directed the jury that there was no evidence that it was the correct battery, and went on to say:

"Mr Catterall was told it was, but you have no evidence about that, and you can't accept, you can't act on what he was told because it's not evidence of the truth of it. You've no evidence that this car had the correct battery, nor is there evidence, expert or otherwise about the electrical configuration of the hybrid vehicles and the batteries that they use and whether they're a possible cause of the fire. So you might think that the extent to which Mr Catterall relied upon what he was told about that, affects the weight that you can give to his opinion. You should bear in mind that if having given the matter careful consideration you do not accept his evidence you don't have to act on it and that's particularly so where the facts upon which his opinion are based is unsupported by other evidence or don't accord with the facts as you find them."

1. In limiting the jury's use of the evidence in this way, his Honour was utilising the provisions of s 136 of the Act. This was appropriate because the evidence of the representations of the Toyota representatives, having been admitted to establish the basis upon which Mr Catterall formed his opinion, was then otherwise able to be used for a hearsay purpose, that is to prove the truth of the facts intended to be asserted by the representation: the Act, s 60. It would have clearly been unfair to the appellant to permit the jury to use Mr Catterall's recitation of what he was told to prove the truth of the facts thereby asserted, when the prosecution had simply failed without explanation to call those witnesses, and they were not identified by Mr Catterall.

Ground 1 - The admissibility of Mr Catterall's expert opinion

"1 That the Learned Judge erred in allowing the evidence of Paul Catterall upon the grounds that the evidence was inadmissible, pursuant to section 76 of the Evidence Act; and

That Section 70 [sic] of the Evidence Act did not apply as the witness's opinions as to:

1. The potential for the 12 volt battery to be a source of ignition; and
2. The witness's conclusions as to the area of origin and the cause of the fire, were conclusions and opinions reached, which were beyond the area of specialized knowledge of the witness."

1. This ground directly attacks the admissibility of the evidence of Mr Catterall. The evidence which must be admissible, and hence is the subject of consideration under this ground, is the evidence given by the witness at trial. Although the evidence of Mr Catterall on the voir dire may well be relevant to the resolution of the issues raised by this ground on the appeal, ultimately the question for the Court is whether the wrongful admission of the evidence has resulted in a miscarriage of justice, Criminal Code, s 402. This question can only be determined by considering the form in which the evidence was adduced before the jury and taking into account any directions from the trial judge as to the use to which the jury may put that evidence. This approach is consistent with that adopted in KMJ v Tasmania [2011] TASCCA 7, 20 Tas R 425 and Standage v Tasmania [2017] TASCCA 23.
2. The ground asserts that Mr Catterall's ultimate opinion as to the source of the fire is inadmissible because it relies, in part, on opinion and facts within the knowledge of others which has not been proved by calling those persons to give evidence. This is an appeal to what at common law may have been called the "basis rule" or "proof of assumption rule". The decision of the High Court in Ramsay v Watson [1961] HCA 65; (1961) 108 CLR 642 was often cited as authority for the proposition that proof of assumed facts was a necessary precondition of admissibility of expert opinion at common law. Whether such a rule was actually identified by that case was a matter of some controversy.
3. In any event, as he must, counsel for the appellant framed his argument within the context of the relevant provisions of the Act. Section 76(1) provides that evidence of an opinion is not admissible to prove the existence of a fact about the existence of which the opinion was expressed (the opinion rule). However, s 79 provides for an exception to the opinion rule in the case of an opinion based on specialised knowledge. In particular, s 79(1) provides as follows:

"(1) If a person has specialised knowledge based on the person's training, study or experience, the opinion rule does not apply to evidence of an opinion of that person that is wholly or substantially based on that knowledge."

1. Mr Doyle, counsel for the appellant, concedes that Mr Catterall had demonstrated specialised knowledge based on his training, study and experience in respect of the identification of the cause and source of fires, and fire behaviour. However, counsel argues that Mr Catterall's opinion in this case was not wholly or substantially based on that knowledge because it was, to an undetermined extent, based on the factual information and/or opinion provided by the unnamed representative of Toyota. These facts or opinions had not been established by admissible evidence, for example, the testimony of the Toyota representative.
2. The question of whether facts upon which an expert relies to form an opinion must be proved by independent evidence as a condition of admissibility under s 79, was considered by the High Court in Dasreef Pty Ltd v Hawchar [2011] HCA 21, 243 CLR 588. In reasons delivered separately from the balance of the court, Heydon J contended for the existence of "the proof of assumption rule" in the operation of s 79. His Honour noted that the proper application of the rule required proof of the factual basis of an opinion as an effective condition of admissibility, because the failure to prove such underlying facts can render the opinion irrelevant, and irrelevant evidence is inadmissible. On the other hand, the plurality (French CJ, Gummow, Hayne, Crennan, Kiefel and Bell JJ) refrained from reading such a requirement into the wording of the section and made it clear that the admissibility of opinion evidence is to be determined by the application of the requirements of the Act. The exception to the opinion rule under s79 applied if the witness had "specialised knowledge based on the person's training, study or experience" and the opinion was "wholly or substantially based on that knowledge". The section does not expressly require proof of underlying factual assumptions. However, as was noted by the New South Wales Court of Criminal Appeal in Taub v The Queen [2017] NSWCCA 198, the plurality also considered that these requirements implied a further condition of admissibility. Their Honours reasoned that the need for the evidence to demonstrate that the opinion is wholly or substantially based on the specialised knowledge of the witness requires an explanation of this relationship in the context of the factual assumptions upon which the opinion is based:

"[37] It should be unnecessary, but it is nonetheless important, to emphasise that what was said by Gleeson CJ in HG (and later by Heydon JA in the Court of Appeal in Makita (Australia) Pty Ltd v Sprowles 2001] NSWCA 305; (2001) 52 NSWLR 705 at 743-744 [85].) is to be read with one basic proposition at the forefront of consideration. The admissibility of opinion evidence is to be determined by application of the requirements of the Evidence Act rather than by any attempt to parse and analyse particular statements in decided cases divorced from the context in which those statements were made. Accepting that to be so, it remains useful to record that it is ordinarily the case, as Heydon JA said in Makita, that 'the expert's evidence must explain how the field of 'specialised knowledge' in which the witness is expert by reason of 'training, study or experience', and on which the opinion is 'wholly or substantially based', applies to the facts assumed or observed so as to produce the opinion propounded'. The way in which s 79(1) is drafted necessarily makes the description of these requirements very long. But that is not to say that the requirements cannot be met in many, perhaps most, cases very quickly and easily. That a specialist medical practitioner expressing a diagnostic opinion in his or her relevant field of specialisation is applying 'specialised knowledge' based on his or her 'training, study or experience', being an opinion 'wholly or substantially based' on that 'specialised knowledge', will require little explicit articulation or amplification once the witness has described his or her qualifications and experience, and has identified the subject matter about which the opinion is proffered."

1. The plurality made it clear that this "third" condition of admissibility did not introduce or re-establish a general rule that necessarily required proof of the underlying factual assumptions of an opinion:

"[41] Contrary to submissions on behalf of Mr Hawchar, this analysis does not seek to introduce what has been called 'the basis rule': a rule by which opinion evidence is to be excluded unless the factual bases upon which the opinion is proffered are established by other evidence. Whether that rule formed part of the common law of evidence need not be examined. It may be accepted that the Law Reform Commission's interim report on evidence Australia, The Law Reform Commission, Evidence, Report No 26, (1985) vol 1 at 417 [750]. denied the existence of such a common law rule and expressed the intention to refrain from including a basis rule in the legislation the Commission proposed and which was later enacted as the Evidence Act 1995 (Cth) and the Evidence Act 1995 (NSW). What has been called the basis rule is a rule directed to the facts of the particular case about which an expert is asked to proffer an opinion and the facts upon which the expert relies to form the opinion expressed. The point which is now made is a point about connecting the opinion expressed by a witness with the witness's specialised knowledge based on training, study or experience.

[42] A failure to demonstrate that an opinion expressed by a witness is based on the witness's specialised knowledge based on training, study or experience is a matter that goes to the admissibility of the evidence, not its weight."

1. The effect of the plurality's reasoning is that evidence of an opinion is admissible if the requirements of the section are satisfied and the connection between the witness's opinion and his specialised knowledge, as it applies to the assumed facts is demonstrated on the evidence. The factual assumptions must therefore be stated and their relationship to the opinion explained, but they need not necessarily be independently proved. The failure to prove facts upon which the expert has relied to form the opinion will therefore not affect the application of s 79 to the evidence, and hence unless the evidence is excluded for another reason, it will be admissible.
2. However, proof, or lack thereof, of the underlying facts will be relevant to the weight of the evidence. As Simpson JA explained in Taub, in the context of consideration of Dasreef:

"[30] The plurality declined to engage with the question whether the 'proof of assumption rule' (what their Honours called 'the basis rule') existed at common law; such a rule, their Honours said, was directed to the facts of a particular case. From that it might be inferred that their Honours considered that whether the facts upon which the opinion was based are established as true is a question that goes not to admissibility, but to the weight to be attributed to the opinion expressed. This is also the analysis of Schmidt J in Kyluk Pty Ltd v Chief Executive, Office of Environment and Heritage (2013) 298 ALR 532; [2013] NSWCCA 114 at [176]- [177].

[31] It seems to me that the difference between Heydon J and the plurality lies in the rigour with which Heydon J would insist on the availability of evidence to prove the truth, or correctness, of the assumptions or facts forming the foundation of the opinion as a condition of admissibility and at the time admissibility is being considered. It is not the position of Heydon J that, before evidence of the opinion could be admitted, it was necessary that the assumptions or facts be proved to be true or correct; rather, it was necessary that it be shown that ultimately the evidence would be capable of establishing that the facts or assumptions were true or correct. To insist on the availability of evidence to prove the truth of the assumptions enhances efficiency of the trial process (see [127]). Whether the evidence succeeds in establishing the truth of the facts is a question for the trier of fact.

[32] The plurality, on the other hand, would allow admission of the opinion evidence provided the reasoning was exposed, reserving to the tribunal of fact whether the evidence was sufficient to establish the truth or correctness of the assumptions or facts. Failure to prove the truth of the assumptions would render the opinion evidence of little or no value."

1. Of course, it is possible to envisage a case in which the failure to prove the underlying assumptions impacts on the admissibility of an opinion. It must, of course, be possible that an opinion completely unrelated to proved facts may be so hypothetical that it simply does not satisfy the test of relevance contained in s 55 of the Act_,_ in that it could not rationally affect, directly or indirectly, the assessment of the probability of the existence of a fact in issue in the proceeding. See IMM v The Queen [2016] HCA 14, 257 CLR 300 at [39].
2. However, provided that the opinion is relevant, even if only tenuously so, and satisfies the conditions of admissibility set out in s 79, the failure to prove underlying factual assumptions may affect the weight to be attributed to the opinion, but not its admissibility. Apart from the extreme case just discussed, weight will never affect relevance, and hence admissibility under s 55. This point was also made in IMM at [40]:

"Because evidence which is relevant has the capability to affect the assessment of the probability of the existence of a fact in issue, it is 'probative'. Therefore, evidence which is relevant according to s 55 and admissible under s 56 is, by definition, 'probative'. But neither s 55 nor s 56 requires that evidence be probative to a particular degree for it to be admissible. Evidence that is of only some, even slight, probative value will be prima facie admissible, just as it is at common law Festa v The Queen (2001) 208 CLR 593 at 599 [14]; [2001] HCA 72."

1. Of course, evidence which is admissible under s 55 may be subject to exclusion under another provision of the Act. In a case where the opinion rule does not exclude the evidence, because the requirements of s 79 have been met, the evidence may still be liable to exclusion under the provisions of ss 135 and 137 of the Act. That issue is the subject of ground 2, and will be considered by reference to that ground.
2. In this case, with respect to the preconditions of admissibility under s 79, Mr Catterall gave unchallenged evidence as to the specialised knowledge he had acquired as a result of training, study and experience. He also explained in some detail the methodology which he employed to arrive at the opinion. Insofar as the opinion relied on his interpretation of the scene and the fire residue, it was apparent that it was substantially based on his specialised knowledge. This included his understanding of fire language and his knowledge as to the tendency of a fire which has commenced internally in a car in which the windows are closed to produce and leave as residue considerable soot, and to extinguish through lack of oxygen. He conducted his own examination of the battery and the electrical componentry in order to identify any indication that the fire may have commenced from that source, and explained that he was looking for evidence of electrical shorting.
3. The only real issue was the extent to which he had relied on information provided to him by Toyota, and the nature of that information in the formation of his opinion. It is true that there was a degree of imprecision in relation to these questions. However, an examination of Mr Catterall's evidence on the voir dire and at trial reveals that the information provided to him was limited to a lack of knowledge on the part of the Toyota person as to any history of spontaneous fire in hybrid vehicles, and identification of the battery from the vehicle as the correct type for that vehicle. It is difficult to understand how the former piece of information could have played any real part in the formation of Mr Catterall's opinion, and he did not suggest that it had. The identification of the battery as the correct battery is a fact asserted by the Toyota dealer and was not otherwise proved. However, in the voir dire Mr Catterall made it clear that he had satisfied himself by independent examination that the battery was not the cause of the fire.
4. The only reasonable view of Mr Catterall's evidence is that he was expressing his own opinion based on his specialised knowledge and, in forming his opinion, had regard to a number of facts, the majority of which were either proved by other evidence or attested to by him. The opinion he expressed was not the opinion of the unnamed representative from Toyota. The only effect of that information was to establish the battery as the correct one for the vehicle. It is a reasonable inference that the significance of this fact in the formation of his overall opinion was limited, particularly when considered in the context of the evidence he gave as to his own independent examination, and other factors which supported his opinion.
5. The partial reliance by an expert on information, factual or otherwise, provided by others, will not impact on the admissibility of the opinion, provided that the opinion is based wholly or substantially upon the expert's specialised knowledge. Whether the opinion is substantially based on such knowledge is a question of degree, and requires an evaluative assessment by the court when determining admissibility. It is inevitable that experts will often rely partially on such information when formulating an opinion. In his submissions, the Director of Public Prosecutions referred to comments of Hall J in R v Jung [2006] NSWSC 658 at [57]:

"[57] It is not uncommon for professional persons or experts in various fields to utilise materials produced by third party specialists for the purpose of assisting them apply their specialised knowledge. That does not mean that the opinion of the former is not based wholly or substantially upon his or her specialised knowledge (the making or production of such materials being proved independently or admitted in legal proceedings). An example is the radiologist who produces an MRI scan which, in due course, is utilised by a medical specialist for the purposes of forming an opinion concerning causation, diagnosis and/or treatment. The specialist utilises such materials (and equipment) for the purposes of exercising his specialised knowledge in order to arrive at an opinion for the purposes of treatment or otherwise. It is apparent from the evidence that Dr Sutisno has, from her experience, an appreciation that photographic images can be affected by issues such as distance between subject and lens, angle, perspective and other issues. Whether or not the ATM photographs and forensic procedures are affected by circumstances that impact upon their quality or utility are matters that go to the soundness or value or integrity of the factual material utilised by her as an expert."

1. When the whole of the evidence of Mr Catterall is taken into account, the only rational inference available is that his ultimate opinion was based wholly or substantially on his specialised knowledge despite his partial use of the Toyota information. Accordingly, the evidence satisfied the requirements for admissibility specified in s 79.
2. The fact in issue, which the prosecution sought to prove by the opinion evidence, was that the appellant had set fire to the vehicle. The fact which the opinion sought to prove, and about which the opinion was expressed, was that the fire had commenced on the external surface of the vehicle, as opposed to having commenced in or around the battery or otherwise internally. This fact, and hence the opinion expressed by Mr Catterall, clearly had the capacity to rationally affect the assessment of the probability of the existence of the fact in issue. Mr Catterall's reliance on some information which had not been otherwise proved in the context of the overall formation of his opinion, did not eliminate the capacity of his evidence to have the required effect. The evidence was therefore relevant. As already noted, it satisfied the requirements of s 79, as explained in Dasreef. Accordingly, the opinion rule did not apply to the evidence of Mr Catterall's opinion. It was, therefore, admissible, subject to any other basis of exclusion, such as ss 135 and 137.

Ground 2 - Should the evidence have been excluded under ss 135 and 137 of the Act?

"2 The Learned Judge erred in failing to exclude the evidence of Paul Catterall as to all discussions and investigations which occurred with, or because of, his discussions with a representative from Toyota, pursuant to section 135, or 137 of the Evidence Act."

1. Both sections 135 and 137 relate to the refusal of a court to admit evidence in a case where the probative value of the evidence is substantially outweighed by the danger that the evidence might be unfairly prejudicial to a party. Section 135 provides for discretionary exclusion, but s 137 is a mandatory requirement. Under that provision, in a criminal proceeding, the court must refuse to admit evidence adduced by the prosecutor if its probative value is outweighed by the danger of unfair prejudice to the defendant.
2. "Probative value" is defined by s 3 of the Act to mean "the extent to which the evidence could rationally affect the assessment of the probability of the existence of a fact in issue". The determination of the probative value of a piece of evidence requires an evaluative assessment. In IMM v The Queen, the majority explained the assessment of probative value as follows:

"[42] Both s 97(1)(b) and s 137 require an assessment of the probative value of the evidence tendered. As mentioned, the Dictionary definition of the 'probative value' of evidence describes evidence which is probative in the same terms as how relevant evidence is described in s 55, namely evidence which "could rationally affect ... the assessment of the probability of the existence of a fact in issue".

[43] The enquiry for the purposes of s 55 is whether the evidence is capable of the effect described at all. The enquiry for the purposes of determining the probative value of evidence is as to the extent of that possible effect. But the point is that in both cases the enquiry is essentially the same; it is as to how the evidence might affect findings of fact. An assessment of the extent of the probative value of the evidence takes that enquiry further, but it remains an enquiry as to the probative nature of the evidence.

[45] The use of the term 'probative value' and the word 'extent' in its definition rest upon the premise that relevant evidence can rationally affect the assessment of the probability of the existence of a fact in issue to different degrees. Taken by itself, the evidence may, if accepted, support an inference to a high degree of probability that the fact in issue exists. On the other hand, it may only, as in the case of circumstantial evidence, strengthen that inference, when considered in conjunction with other evidence. The evidence, if accepted, may establish a sufficient condition for the existence of the fact in issue or only a necessary condition. The ways in which evidence, if accepted, could affect the assessment of the probability of the existence of a fact in issue are various."

1. Their Honours went on to conclude that, for the purposes of the assessment, it should be assumed that the jury will accept the evidence, having regard to both its credibility and its reliability. In other words, in conducting the evaluative assessment of probative value, the evidence should be taken at its highest in terms of its capacity to affect the assessment of a fact in issue, and the trial judge should ignore issues of credibility and reliability. This basis of assessment was noted to apply specifically to the assessment of probative value for the purposes of s 137:

"[47] In comparison, the requisite probative value of the evidence is not spelled out in s 137. It requires the 'probative value' of the evidence to be weighed against the danger of unfair prejudice to the defendant. This again requires that the evidence be taken at its highest in the effect it could achieve on the assessment of the probability of the existence of the facts in issue."

1. The relevance of the reliability of the evidence to the assessment was further considered at [52]:

"[52] Once it is understood that an assumption as to the jury's acceptance of the evidence must be made, it follows that no question as to credibility of the evidence, or the witness giving it, can arise. For the same reason, no question as to the reliability of the evidence can arise. If the jury are to be taken to accept the evidence, they will be taken to accept it completely in proof of the facts stated. There can be no disaggregation of the two - reliability and credibility - as Dupas v The Queen may imply. They are both subsumed in the jury's acceptance of the evidence.

1. Finally, the majority observed at [57] that to the extent that reliability is relevant to the application of s 137, it falls to be considered in respect of the risk of prejudice, not as part of the assessment of the probative value of the evidence.
2. A strict application of these observations would suggest that the failure to establish the facts upon which the opinion is based will not affect the assessment of probative value for the purposes of ss 135 or 137. If an assumption is made that the witness's opinion will be accepted by the jury, then the only real question is the extent to which the fact about which the opinion was expressed could rationally affect the assessment of the probability of the existence of a fact in issue. In this case, that must mean the extent to which Mr Catterall's opinion that the fire was highly likely to have originated at the rear and on the external surface of the vehicle, affected the assessment by the jury as to whether the appellant was responsible for the fire. In making this assessment, the trial judge was entitled to consider the significance of the evidence in the context of other evidence presented by the prosecution. This included the improbable coincidence that the fire started spontaneously at the precise moment that the appellant is seen on the CCTV footage walking away from the vehicle, particularly having regard to the evidence that the vehicle had been parked in that location for several hours by that time. On any reasonable view of the prosecution case, on the assumption that the jury accepted Mr Catterall's opinion in proof of the fact about which the opinion was expressed, that is, that the fire had started on the external surface of the vehicle, it was highly probative of the fact in issue, that is, that the appellant had started the fire.
3. An aspect of the reasons of the majority in IMM which is somewhat difficult to reconcile with the comments from those reasons quoted above, is their Honours' reference at [50] to the "weak identification" example and the suggestion that the deficiencies surrounding an identification would impact on the assessment of the probative value of such evidence. On one view, the aspects of an identification which make it weak are matters which affect the reliability of the evidence, and, hence, ought not be considered when assessing the probative value of the evidence. However, if those aspects are relevant to the assessment of probative value, as the said example suggests, then, by analogy, unproved or discredited assumptions which form the basis of an opinion would be relevant to the assessment of the probative value of that opinion. However, in this case, even if the assessment of probative value was to take into account the failure to independently establish the Toyota information, in particular, the suitability of the battery for the vehicle, it must still be the case that this evidence has a high degree of probative value. While the failure to call the representative from Toyota to prove the relevant facts must necessarily have some impact on the probative value of the opinion, it is necessary in the assessment of this question to consider Mr Catterall's opinion in the context of the whole of his evidence, and the evidence generally. As already noted, Mr Catterall based his opinion on a considerable body of fact, much of which had been established by his or other evidence. This included:
   • The fire language indicators which supported the conclusion that the fire had commenced externally and at the rear of the vehicle.
   • The broken rear window which was consistent with the fire having commenced externally and then moving to the interior.
   • The interior fire language.
   • The absence of soot residue on the windows, which tended to be inconsistent with the fire having commenced internally.
   • Mr Catterall's own examination of the battery and the electrical circuitry, and the absence of indications which would be consistent with the fire having commenced in those areas.
   • The information provided to him by Mr Parker, which had been confirmed in Mr Parker's evidence, and was consistent with the fire having commenced externally at the rear of the vehicle.
4. On an overall view of this evidence, even if allowance is made for the unproved facts asserted by the Toyota information, the opinion of Mr Catterall had significant probative value.
5. Sections 135 and 137 also require consideration of whether the admission of the evidence carries a danger of unfair prejudice to the appellant. The concept of unfair prejudice was explained by Crawford CJ in Neill-Fraser v Tasmania [2012] TASCCA 2 at [184]:

"[184] When considering the danger of unfair prejudice, care must be taken not to confuse prejudice with unfair prejudice. Too often, defence counsel fail to distinguish between them. All evidence that may tend to convict an accused person is prejudicial, but that does not mean that it is unfairly prejudicial. What is meant by unfair prejudice is that the jury may use the evidence to make a decision on an improper, perhaps emotional basis. If there is a real risk that the evidence may be misused by the jury in some way, then it may be unfairly prejudicial. R v BD (1997) 94 A Crim R 131 at 139, 151."

1. In this case, the risk of misuse arises from the possibility that the jury may not have properly factored into its assessment of the weight of Mr Catterall's opinion, the impact upon it of the absence of proof of the Toyota information. Such a risk arose in this case because of the imprecision in the evidence as to the precise role which the relevant information played in the formation of Mr Catterall's opinion.
2. While it would clearly have been desirable for attention to be addressed to this question in leading the evidence of Mr Catterall, particularly given that it was known when he gave his evidence that the Crown had no intention of calling the person to whom he had spoken at Toyota, nor proving those matters in any other way, the danger of unfair prejudice arising from this evidence was relatively low. An overview of Mr Catterall's evidence demonstrates that he confined the use of this information to an early consideration of the possibility that the fire had occurred through electrical malfunction. His evidence went on to explain that he had performed investigations to exclude this possibility and had formed an opinion on the basis of the other considerations referred to above. Further, in cross-examination, he confirmed with defence counsel that the opinion concerning the fire starting externally was a probability, not a certainty. Finally, the trial judge clearly explained to the jury that the information had not been proved, and that it should not act on the basis that that information was true. If one accepts that the jury followed this direction, then having regard to the other evidence which supported Mr Catterall's opinion, it can be seen that the jury would still have been justified in accepting that opinion. It is appropriate to take into account directions by the trial judge when assessing the danger of unfair prejudice: Standage v Tasmania (above). In assessing the effect of jury directions, it should be assumed that "as a general rule, juries understand, and follow, the directions they are given by trial judges": Gilbert v The Queen [2000] HCA 15, 109 A Crim R 580 at [13]; Sio v The Queen [2016] HCA 32; Marshall and Richardson v Tasmania [2016] TASCCA 21, per Brett J at [63]-[65].
3. There is a further matter that arises in relation to unfair prejudice. At the point of determining the admissibility of the evidence, the trial judge was entitled to assess this question on the basis of the evidence presented at the voir dire. In that evidence, Mr Catterall went into considerable detail about the role that was played by the Toyota information. As already noted, in cross-examination he was challenged extensively about the role that this information played in the formation of his opinion. He was clear that although initially he was concerned about the possibility of the fire originating from the electrical system, he was able to discount that possibility, relying on his own investigations as detailed above. The effect of the evidence was that the information set him on the correct investigative path, but ultimately had little effect on the formation of his final opinion. This evidence was not repeated in the evidence before the jury, largely because Mr Catterall was not challenged about this question by defence counsel. It may well be that defence counsel did not pursue that line of questioning as a forensic choice, having regard to the answers given by Mr Catterall on the voir dire, but that is of little importance. The significance of the evidence on the voir dire is that the trial judge was aware of Mr Catterall's evidence concerning the actual role played by the Toyota information in the formation of his opinion. The trial judge was therefore entitled to conclude that any risk that the jury might assume the truth of the Toyota information would have little impact in their overall assessment of the importance of the opinion evidence of Mr Catterall because, whether the evidence was true or not, ultimately had little importance in the formation of his opinion. In fact, it could be argued with the benefit of hindsight, that the trial judge's directions to the jury concerning the use of the evidence placed greater importance on this information and, accordingly, had greater potential to undermine the jury's acceptance and use of Mr Catterall's opinion, than was actually warranted. Whether that is the case or not, the trial judge was entitled to use the voir dire evidence when assessing the question of unfair prejudice, and entitled to regard it as obviating to a considerable extent the danger of misuse of the evidence.
4. I am satisfied that the probative value of the evidence was not outweighed by the danger of unfair prejudice and the trial judge correctly concluded so. Accordingly, there was no basis upon which the evidence could have been excluded under ss 135 or 137 of the Act.

1. It follows that the evidence was properly admitted. There has been no miscarriage of justice. I would dismiss the appeal.