The significance of the DNA evidence will depend critically upon what else is known about the suspect. If he has a convincing alibi at the other end of England at the time of the crime, it will appear highly improbable that he can have been responsible for the crime, despite his matching DNA profile. If, however, he was near the scene of the crime when it was committed, or has been identified as a suspect because of other evidence which suggests that he may have been responsible for the crime, the DNA evidence becomes more significant. The possibility that two of the only 26 men in the United Kingdom with the matching DNA should have been in the vicinity of the crime will seem almost incredible and a comparatively slight nexus between the defendant and the crime, independent of the DNA, is likely to suffice to present an overall picture to the jury that satisfies them of the defendant's guilt."
23 The first part of this passage identifies the prosecutor's fallacy, explaining that the statistical probability within the relevant population does not translate to the same statistical probability for a given member of the population. The second part of the passage goes to a corollary, that even with a correct understanding of the statistical probability the significance of the DNA statistical evidence will depend on other evidence.
24 As the explanation applies in the present circumstances, the move from (i) to (ii) above left out of account that within the Australian population there could statistically be other matings producing the DNA profile found in the bones; and further, attention can not be confined to the Australian population. If the bones are 660,000 times more likely to be those of a child of Mrs Strachan and Mr Baan than of the child of a random mating in the Australian population, there will still be a number of random matings in the Australian population producing the DNA profile found in the bones; and because the child whose bones were found at Tregear could have been conceived anywhere in the world, there could be many matings not in the Australian population producing the DNA profile found in the bones.
25 If attention is confined to the Australian population, a rough calculation of the kind undertaken in Doheny and Adams is difficult because conception of a child at an unknown time whose bones might have been those found at Tregear in 1991 is not the same as leaving a crime stain at Tregear in 1991. But on any view the relevant Australian population at the time of the random matings must be many times 660,000. The Crown accepted that statistically there could be maybe thirty random matings in the Australian population producing the DNA profile found in the bones. If so, and I take up the figure only as an illustration, Phillips LJ might have said that there was a statistical probability that the bones were the bones of Mrs Keir of something like 30:1. I would prefer not to put it that way, if for no other reason than because that can lead to failing to pay regard to the other evidence bearing upon probability, but it starkly illustrates the difference from a presentation of odds of 660,000:1. Using the same figure, what the DNA statistical evidence meant was that only about thirty persons in Australia had the DNA profile found in the bones; and then the significance of that had to be determined in the light of the other evidence bearing upon whether the bones found at Tregear were likely to have been those of Mrs Keir or those of one of the statistical other twenty-nine persons. The jury was likely to be greatly impressed by the figure with all the noughts, and to be misled into overlooking the number of other persons with the DNA profile found in the bones and failing to attend to the other evidence.
26 But in this case attention could not be confined to the Australian population. What the DNA statistical evidence meant was more complex, for that reason and because of the range of possible times of conception. If regard were had to the world population, there could be many more persons with the DNA profile found in the bones.
27 The trial judge was repeating what the Crown had put in submissions. As will be seen, counsel for the appellant did not recognise the prosecutor's fallacy and ask that it be corrected. By 1999 the prosecutor's fallacy had been sufficiently discussed in legal writings that warning bells should have rung. Unfortunately, they did not sound in the ears of the trial judge, who also did not recognise the prosecutor's fallacy and endeavour to correct it. In the result, the jury was left to assess whether the bones were those of Mrs Keir, and so to determine whether Mrs Keir was dead and had been killed by the appellant, and specifically the reliability and credibility of the identification evidence, by regard to a misleading and prejudicial criterion.
28 Counsel for the appellant asked for a redirection, but only in relation to the identification evidence and not on the ground that the prosecutor's fallacy had intruded.
29 The transcript first records -
"Also the connection between the probability of DNA and identification by Jennifer Soler. I would submit that the directions required a very discrete consideration of the identification of Jennifer Soler and that this connection means that the jury could fall into error in essentially combining these two pieces of evidence to in fact almost by the bootstraps so to speak, bearing in mind that, so far as the probability is concerned, that 660,000 to one is not a way in fact, that they should look at the identification evidence, that it should be looked at in a discrete way, in identification that she in fact had raised.
HIS HONOUR: So you think in considering whether her identification was reliable they should disregard all the other evidence in the case?
ZAHRA: I would submit it is dangerous to connect these two pieces of evidence in some way.
HIS HONOUR: Can you deal with my contention first?
ZAHRA: I don't suggest that. It is only a question of accommodation.
HIS HONOUR: Then the question is what is the other evidence in the case to use, which they can analyse to suggest that her evidence was right? I was merely pointing out this was one part of the evidence and this was the most significant one.
ZAHRA: My submission is that it is dangerous to look at the DNA evidence and seek to combine it with the other evidence and come up with a conclusion about the accuracy of her evidence. I submit there are many other factors to consider when giving her evidence weight.
HIS HONOUR: Such as what?
ZAHRA: The fact that she had known Jean Keir for quite some time in circumstances where there was a close relationship, the identification on the particular day, particularly in relation to the identification of the hair, the showing of the photograph.
HIS HONOUR: I brought that to the jury's attention."
30 Later the transcript records -
"The other aspect is in relation to Jennifer Soler's evidence, identification evidence, where your Honour had looked at that piece of evidence with the DNA evidence and my submission was that it should not be confined in that way because the jury may misdirect themselves to properly applying the acceptable principles of the facts to be considered in identification - it was not a matter to look at that - it is not a matter to look at Jennifer Soler's evidence as a statistical probability. The important matters are no doubt the matter of the previous association and the time she had her under review and those matters are relevant.
HIS HONOUR: Are you submitting they should not take into account the conclusion which they might draw from the DNA evidence that it - I didn't use this word to them but assume they did - that it was virtually certain that those bones were Jean Keir, but are you saying they couldn't use their view of the likelihood that those bones were those of Jean Keir to consider whether they accepted the reliability of the evidence of Jennifer Soler?
ZAHRA: Your Honour what I submitted yesterday, there would be a need of degree of caution in a sense to cross-pollinate these two particular aspects because the question of identification is in fact quite a complex one in the sense there are various facts they would need to weigh-up quite independently and that is obviously the particular relationship between Miss Soler and Jean Keir, the method by which she was able to identify Jean Keir at this point of time, together with the evidence in this Court of the photographs, so it should be considered in a discrete way, that caution should be exercised in cross-pollinating both, but it is important that they consider also the weight of the evidence of Miss Soler. In fact the opposite would occur. If obviously they were satisfied that Jennifer Soler did in fact identify Jean Keir,then obviously that may reflect also on the DNA evidence but it is important for this identification to at least in some way --
HIS HONOUR: They may need to decide which they prefer?
ZAHRA: Yes, that's right.
HIS HONOUR: But if they come to a view about the DNA evidence and accepted that indeed it did show those odds, are you submitting to me this, they should not bear that in mind when considering Jennifer Soler's---?
ZAHRA: No, only a degree of caution should be exercised when considering her evidence.
HIS HONOUR: That's precisely what I said in relation to the scientific evidence.
ZAHRA: That's what I said yesterday afternoon, that your Honour should tell them they should be minded to look at these as discrete matters before considering the aspect of the evidence together."
31 What counsel said was at times unclear, and seems to have changed, but it was not that there had been the impermissible move from (i) to (ii) above. There may have been complaint about using the DNA statistical evidence at all as a criterion for the reliability and credibility of the identification evidence, a matter which need not be addressed in these reasons. At least there was raised the need to ensure that the probability ratio was seen as part only of the evidence, and evaluated in the light of the totality of the evidence. That was the subject of the second part of the passage from Doheny and Adams set out above. But what counsel said did not touch what was there first addressed, the erroneous appreciation of the significance of the probability ratio under the influence of the prosecutor's fallacy.
32 The trial judge did give a further direction, saying -
"I reminded you of the evidence of Jennifer Soler and I pointed out to you that you should not look at this evidence by itself and in a stark way I pointed out that if you accepted the DNA evidence that there was a 660,000 chance to one that these bones were not those of Jean Keir then that would lead you to look at Jennifer Soler's identification with some scepticism.
Ladies and gentlemen, I think there are a number of things I should say about that. First of all, of course, what I was really intending to do there was to point out that you don't look at each piece of evidence as a compartment but you do look at each piece of evidence.
Mr Zahra submitted to you and the defence case is well, if you looked at Jennifer Soler and having regard to the fact that she knew Jean Keir, that she was sure that it was Jean Keir, that she had an adequate opportunity to observe the woman she identified as Jean Keir, that she not only got the face right, says Mr Zahra, but also got the hair right. If you started from that line it might lead you to doubt for example the DNA evidence.
Well it is a matter for you as to what parts of the evidence you rely on as being reliable but in dealing with this mater of course you don't only look at the DNA evidence; you look at the whole of the evidence in the case and you weigh-up each piece of evidence by looking at the whole, what you accept and what you don't.
I think in fairness to the Crown you will recall that I pointed out Mr Bernard Shaw's statement about lies, damn lies and statistics. In this case, however, there is no suggestion that the statistics are false or misleading. They of course don't amount to certainty. They were statistics concerned about probabilities and there was no cross-examination directed to Mr Goetz - I wrongly called him Doctor - to Mr Goetz that suggested that the statistical process was unfair, unreasonable, not arithmetical, not reliable - no suggestion of that in this case - but what I am saying to you is that what it indicates is that it is a very high degree of probability indeed , you might think, and that if you were persuaded that that was reliable and that there was no contamination of that the reasonable possibility of contamination could be dismissed, I did suggest to you that that evidence, because it is objective, is a very useful compass or a very useful standard by which you look at other areas in the case." (emphasis added)
33 As I have indicated, the Crown submitted that this rectified the error in the earlier directions, because the jury was reminded that the evaluation of DNA evidence was a matter for them in the light of the totality of expert and non-expert evidence. Whether it was sufficient as such a reminder need not be decided, but it did not rectify the error. The prosecutor's fallacy was still not recognized. The misuse of the statistical probability was not corrected in relation to the identification evidence or otherwise, and more, was reinforced in relation to the identification evidence by the trial judge referring to "a 660,000 chance to one that these bones were not those of Jean Keir …" and suggesting in that connection that the jury could see the statistical process as indicating "a very high degree of probability indeed". If it was proper to leave the jury with odds at all, the jury was left with the potentially misleading odds of 660,000:1 and without guidance on what the DNA statistical evidence really meant.