The following is an extract from Expert Evidence: Law, Practice and Procedure, 2nd Edition
. To find out more about this highly regarded book, or to order a copy, click here
Scientific evidence is rarely the only prosecution evidence. It generally forms part of the matrix of facts which the prosecution seeks to suggest properly leads to a finding beyond reasonable doubt that the accused person committed the crime. Frequently, scientific evidence reduces down to statistical evidence which, when adduced by the prosecution, raises the likelihood that the accused person is the offender. This raises the difficult issue of the use to which the trier of fact, be it a judge, magistrate or a jury, can legitimately put scientific evidence.
In a series of DNA profiling cases, courts have held that scientists ought not to be asked questions whose answers the jury might misconstrue, such as the likelihood that it was the defendant who left the crime stain: Doheny and Adams v The Queen
 1 Cr App R 369; Latcha v The Queen
(1998) 104 A Crim R 390 at 397. However, it is standard for the jury to be provided with the random occurrence ratio—the frequency with which the matching DNA characteristics are likely to be found in the population at large. This provides it with a tool by which to evaluate the significance of the match between the crime scene DNA and that of the accused. These figures vary dramatically, sometimes being very low by reason of only one probe, for instance, being able to be used, other times being high. In general, the prosecution is allowed to adduce such scientific evidence in the same way that it was previously entitled to adduce ABO blood typing evidence, even though the statistics yielded from such testing often only modestly advanced the prosecution case.
The issue for a decision-maker in a criminal trial, when such evidence is equivocal, or of modest dimensions of assistance to the prosecution, is to determine what use can be made of the evidence. It has been held that a jury is obliged to consider ‘‘the weight which is to be given to the united force of all the circumstances put together’’: Belhaven and Stenton Peerage
(1875) 1 App Cas 278 at 279. This means that a jury should decide whether it accepts the evidence of a particular fact, not by considering the evidence directly relating to the fact in isolation, but in the light of all of the evidence. It is entitled to draw an inference of guilt from a combination of facts, none of which viewed alone would support that inference: Chamberlain v The Queen (No 2)
(1984) 153 CLR 521 at 536 per Gibbs CJ and Mason J. An inference of guilt in a criminal trial can be drawn if it is based upon primary facts which are found beyond reasonable doubt and if it is the only inference which is reasonably open upon the whole body of primary facts: Chamberlain v The Queen (No 2) (1984) 153 CLR 521 at 598 per Brennan J; at 536 per Gibbs CJ and Mason J; see also Moss v Baines
 WAR 7 at 11. An inference of guilt may properly be drawn, although any particular primary fact, or any concatenation of primary facts falling short of the whole, would be insufficient to exclude other inferences.
The High Court’s decision in Chamberlain v The Queen (No 2)
(1984) 153 CLR 521 provides a good example of such a difficulty. The prosecution relied on a number of different groups of evidence:
- (1) evidence of foetal haemoglobin in the car of the accused and in their camera case;
- (2) evidence of likely bleeding if a dingo had seized the baby’s head and of the absence of large quantities of blood in the tent in which the deceased had been at the time; and
- (3) evidence of the condition of the deceased’s jumpsuit and singlet and the arrangement of the deceased’s clothes when they were found.
One of the issues for the High Court was whether the fact that the foetal haemoglobin evidence was flawed meant that the jury verdict should be quashed.
Gibbs CJ and Mason J drew a distinction between crucial (or primary) facts and secondary facts, both of which have the potential to be proved by scientific evidence:
‘‘[T]he jury cannot view a fact as a basis for an inference of guilt unless at the end of the day they are satisfied of the existence of the fact beyond reasonable doubt. When the evidence is circumstantial, the jury, whether in a civil or in a criminal case, are required to draw an inference from the circumstances of the case; in a civil case the circumstances must raise a more probable inference in favour of what is alleged, and in a criminal case the circumstances must exclude any reasonable hypothesis consistent with innocence’’: at 536.
It is not possible for a decision-maker in a criminal case to be satisfied beyond reasonable doubt of an inference drawn from facts about the existence of which he or she is in doubt.
Deane J in Chamberlain took a somewhat different approach, finding that it is not the law that a juror is precluded in all circumstances from drawing an inference from a primary fact unless it is proved beyond reasonable doubt. However, if a primary fact constitutes an essential element of a crime charged, a juror must be persuaded that that fact has been proved beyond reasonable doubt before properly joining in a verdict of guilty. He found that those bodies of evidence were cumulative:
‘‘The jury was entitled to pay regard to all of them, even if unpersuaded that any or all of them was proved beyond reasonable doubt. Thus a conclusion that the evidence directed to showing the presence of foetal haemoglobin in the car was persuasive only to the extent of balance of probability does not mean that the conclusion and the evidence should be rejected as irrelevant. Even though the evidence, viewed discretely, does no more than establish the presence of foetal haemoglobin on the balance of probabilities, it remains part of the totality of the admissible and relevant evidence in the context of which the ultimate question whether Mrs Chamberlain’s guilt was established beyond reasonable doubt fell and falls to be determined’’: at 627.
Thus in Chamberlain v The Queen (No 2)
(1984) 153 CLR 521 the High Court found that although scientific evidence that blood under the dashboard and in the car of the accused parents was foetal blood and the evidence of a pathologist that he saw on the jumpsuit of the deceased the imprint of a hand in blood were unsafe to form the basis of an inference of guilt, the jury’s finding of guilt should not be disturbed because of the existence of other legitimate bases for its decision.
In R v Anderson
 1 VR 1 at 26 the Victorian Court of Appeal applied the same principle to insist that a jury should have been instructed that it could only accept the opinions expressed by two treating doctors that wounds on the accused had been self-inflicted, to the exclusion of opinions on the same subject expressed by a forensic physician and a forensic pathologist, if satisfied beyond reasonable doubt that the former opinions were correct: see also R v Sodo
(1975) 61 Cr App R 131 at 134.
As a further example of the principles, in R v Van Beelen
(1973) 4 SASR 353 it was decided by the South Australian Court of Criminal Appeal that it had been illegitimate for a jury to find an accused man guilty of murder when it could only have done so on the basis of scientific evidence that was equivocal. In Van Beelen the direct evidence in respect of the murder charge was insufficient for a finding of guilt without scientific evidence. The scientific evidence, though, only went as far as to establish that certain trace materials (fibres, foraminefera, paint chips and hairs) found on or about the deceased were similar to other trace materials found on or about the accused man. For instance, fibres found on the deceased girl’s singlet were said to be similar to those from the pullover of the accused man.
The court held that there had been sufficient evidence to support the jury’s finding of guilt. It had been legitimate for the jury to infer, from the fact that in a number of instances the trace materials on the deceased and on the accused could have originated from the same source, that they did so originate. This was so notwithstanding that the individual identity of any one set of trace materials, considered in isolation, was not proved beyond reasonable doubt. However, the Court of Appeal found that the trial judge had erred in directing the jury that it could in effect draw an inference of guilt from primary evidence as to whose existence it was in doubt. It held:
the jury is not, in our view, required to split up the various stages in the process of reasoning leading to the conclusion of guilt beyond reasonable doubt and to apply some particular standard of proof to each of those steps ....That, of course, does not mean that they ought to be encouraged or permitted to draw inferences of guilt from doubtful facts. As a matter of common sense it is impossible to infer guilt beyond reasonable doubt from facts which are in doubt. There is a clear distinction between drawing an inference of guilt from a combination of several proved facts, none of which by itself would support the inference, and drawing an inference of guilt from several facts whose existence is in doubt. In the first place the combination does what each fact taken in isolation could not do; in the second case the combination counts for nothing’’: at 374.