The voir dire
20 Mr Garling submitted that opinion evidence presented in this form was irrelevant, and therefore inadmissible. He referred to s 56(2) of the Evidence Act 2004 (NI) ("Evidence Act 2004"), and relied upon the fact that Dr Melton had used a North American database which had not been shown to be applicable to the population of Norfolk Island.
21 Alternatively, Mr Garling submitted that Dr Melton's evidence should be excluded in the exercise of the Court's discretion under s 135(a) and (b) of the Evidence Act 2004. He initially submitted that the probative value of her evidence was substantially outweighed by the danger that it might be unfairly prejudicial to the accused. However, he subsequently clarified that submission and indicated that by "prejudicial" he meant the danger separately identified in s 135(b) that the evidence might be misleading or confusing.
22 Because I had great difficulty in understanding Dr Melton's two reports, and her replies by email to the questions posed by the Crown, I was uncertain what evidence she would actually give if she were called to testify before the jury. Mr Howard SC informed me that he had spoken to Dr Melton after her arrival on Norfolk Island, and he understood that she could "clarify in more detail" the conclusions set out in her various written comments. I therefore determined that there should be a voir dire.
23 In the course of that voir dire Dr Melton first indicated that she had had the opportunity, since arriving on Norfolk Island, to read reports prepared by Dr John Buckleton and Susan Vintiner in connection with this trial. She had also had the opportunity to read an article by Dr Buckleton concerning specific genetic testing that had been done on the Norfolk Island community in relation to cardiovascular disease. She said that in the past she had studied the mitochondrial DNA profiles of Polynesian populations. She was also familiar with the mitochondrial DNA profiles common to, and expected of, various racial groups including Africans, Asians and Caucasians.
24 Dr Melton next explained that she had used a "consensus profile" which showed the common findings at particular nucleotide positions. She stated that the profiles obtained for hairs Q1, Q4 and Q5 had many things in common. However, they also had some slightly different mixed sites. Dr Melton said there could be two explanations for the different mixed sites. The first would be contamination, and the second would be that the mitochondrial DNA had been damaged in the time after the hairs were initially deposited. In her view, the second explanation for the mixed sites was to be preferred.
25 Dr Melton agreed that there was no mitochondrial DNA database in Australia or New Zealand. It was for that reason that she had used the North American database. She explained that given what she knew of the genetic make-up of the Australian and New Zealand population, she would have expected similar levels of diversity in the Caucasian population as were found in North America and Europe.
26 She said that she detected either an Asian or African element in the mitochondrial DNA profiles that she obtained. She said that she would not have expected to have obtained such a profile from many members of the Norfolk Island community. In her own words, Dr Melton said (at Tx 21):
"We don't want to overstate the constraints of what we know, but my anticipation is, based on the fact that when you sample any population you have high diversity, that we would not expect to find this profile at extremely high frequency. We cannot put a statistic on it because we don't have a representative database, but we would say that these three hairs have the same type as Janelle Patton and, as in all DNA testing, the language "cannot exclude" is used - "
27 When asked to clarify what she meant by the term "cannot exclude", Dr Melton continued (at Tx 21):
"Well it means that there is a pool of individuals that has the type that Janelle Patton has, including her maternal relatives, her known maternal relatives, and in theory people who are not apparent maternal relatives somewhere in the population. If you think about your own maternal lineage, if you go back five or six generations, you don't know who your maternal relatives are. There could be in theory people in the world with your mitochondrial DNA type.
The way we place a context on that is by understanding what databases of what mitochondrial DNA types look lie [sic]. Are there pools of types in various populations. Are there types that are unique to one population and not to others. And so we say she's not excluded. By that we mean there is a pool of people that has her type."
28 Dr Melton was then asked the size of the pool. She said it was "very small". When asked what that meant, she replied that generally speaking, mitochondrial DNA produced frequency results that were very low, of the order of one to two percent or less. When asked why she persistently spoke in terms of an inability to exclude, rather than saying that it was highly likely that the hairs came from the same maternal line, she replied that this was historically the way in which mitochondrial DNA results were reported.
29 Dr Melton said that mitochondrial DNA was not, and never would be, as discriminating as nuclear DNA. However, she added that it was more discriminating than blood typing. She declined to be drawn into any statistical evaluation, insisting that all that she could say was that "some percentage of the population" would be expected to have this profile. She said there were two reasons why she would not proffer a statistic. The first was that she had no specific database applicable to Norfolk Island, although she said other available databases all had approximately the same high diversity make-up. The second was that the hairs that she examined had mixed sites, and mitochondrial DNA experts did not do statistics on mixtures.
30 It is fair to say that, at various points during the course of her evidence on the voir dire, Dr Melton was prepared to say that the particular profile that she had discerned was not likely to be common. She agreed that she was basing that opinion upon her knowledge of the historical genetic make-up of "this part of the world". She said that she did not believe that she would find this profile in "20, 30 and 40 per cent of the population". However, when pressed as to whether she could or would go further if permitted to give evidence before the jury, she returned to the mantra that she would only be able to state that Janelle Patton and her maternal relatives could not be excluded as donors of hairs Q1, Q4 and Q5. She said (at Tx 27):
"That is the appropriate terminology for mitochondrial DNA. I'm very careful to explain to juries that we can never say for sure these are her hairs, but that these hairs do have the profile that she has and that this is how many times we saw this profile in our database and this is the ethnicity determination of these profiles, and that's basically what I would say."
31 Dr Melton agreed, under cross-examination, that she had never used terms such as "highly unlikely" when dealing with mitochondrial DNA that contained mixed sites. She said that in such cases she would say no more than that she "could not exclude". She said that she would be prepared to tell the jury that Ms Patton had rather unusual ethnicity (there being some Asian or African influence in her mitochondrial DNA). However, she repeated that she would only tell the jury that these were the ethnicities associated with this profile and "as in all mitochondrial DNA cases … allow the jury to make their own conclusions regarding how they would like to interpret that".
32 Dr Melton added (at Tx 31):
"All I can do is answer questions to the best of my knowledge and honestly, and the terminology of mitochondrial DNA testing here and everywhere I'm aware of is that you cannot exclude, and then to provide a context for that failure to exclude. So that's what I intend to do."
33 Her evidence continued as follows (at Tx 32-34):
"A. I would say that we cannot place a statistical likelihood on this because we do not have currently a representative database for this part of the world. However, the profile is the same as Janelle Patton's profile, the consensus profile is, and therefore we cannot exclude, and that is the nature of all mitochondrial DNA evidence.
Q. Would you say it's 99 per cent likely to be hers?
A. That's not the way mitochondrial evidence is given.
Q. Would you say it's 60 per cent likely to be hers?
A. I cannot say that.
Q. Would you say it's 50 per cent likely to be hers?
A. No. We'd never give evidence that way in mitochondrial DNA testing.
Q. I am just testing what you can and cannot say, doctor.
The next question I want to ask you is the expression "she and her maternal relatives", a common expression in mitochondrial DNA for the reasons that you explained, that it's passed down the maternal line?
A. Yes.
Q. How many people are we talking about in that group - she and her maternal relatives?
A. I don't know.
Q. It could be thousands?
A. Unlikely for the known maternal relatives to be thousands, although it's possible. I don't know.
Q. Can you give me a maximum number it might be?
A. No.
Q. Could you give me a minimum - I suppose you can give me a minimum number: a mother and daughter would be the minimum, I suppose?
A. That's correct, and obviously we would consider all the other factors in the case as well, as mitochondrial DNA never stands alone, it stands in addition to other information in the case.
Q. Doctor, you are only giving the bit about mitochondrial DNA?
A. That's correct.
Q. We can leave the rest of the case to the jury.
A. Correct.
Q. What I want to know is if I asked you how many people are in the group of Ms Patton and her maternal relatives, you couldn't give a number?
A. No.
Q. All you can say is it is potentially a large number, but you don't know?
A. Or potentially a very small number.
Q. You just have no idea?
A. I do not know.
Q. Is it right to understand that the same mitochondrial DNA can go back many generations?
A. Many generations, yes.
Q. Is there a limit, to your knowledge, on the number of generations it can go back?
A. No.
Q. So it is an unlimited number of generations?
A. Correct.
Q. There are some studies that have gone back, to your knowledge, at least 24 or 25 generations, aren't there?
A. That's correct.
Q. Used in that term by scientists, is a generation thought to be 20 years or --
A. Approximately 20 to 25 years.
Q. Twenty to 25 years?
A. Yes.
Q. So if we're talking of 25 generations, somewhere between 500 and 600 years; is that right?
A. Yes."
34 For completeness, I should add that Dr Melton was re-examined and then recalled, at the request of the Crown, in an effort to elicit from her a more precise answer to the question of what she would say to the jury if allowed to give evidence. Her evidence did not take the matter further. She insisted that she would be forced to say that she could not exclude the possibility that the hairs in question came from Janelle Patton, or her maternal relatives, using the same terminology as she did in all mitochondrial cases. She said that she could not give any indication of how frequently she would expect to find a profile such as that discerned in the context of Norfolk Island. She said (at Tx 48) that she could not give a number of any kind, but would say that it would "not be likely to see this profile endemic on the island in high frequency".
35 Despite Mr Howard's best efforts, Dr Melton persisted in using language of this kind when asked specifically what she would say to the jury if her evidence was admitted.