Andrew Haesler SC Show This paper is an updated version of papers prepared for the Judicial Commission of New South Wales, and later published in the Judicial Review, (2008) Vol 8 No 1. Introduction DNA Deoxyribonucleic acid matching is a wonderful investigative tool. DNA evidence can provide powerful evidence in support of a prosecution case. DNA evidence can also provide convincing evidence of a person’s innocence. A profile taken from the DNA of a suspect can be compared with the profile of a sample of DNA taken from a crime scene. It may, depending on the other evidence, be compelling evidence of guilt. Profiles can be stored on a computer database. They can be easily cross-checked and any linkage investigated. A statistically validated “match” or “link” between these profiles is evidence that they come from the same source. DNA is corroborative evidence. It is particularly useful if supported by statistics that the chance of someone else other than a defendant leaving the crime scene stain is highly unlikely or highly improbable, by a ratio of one in ten billion. DNA evidence can, however, be misunderstood. If unchallenged, DNA evidence can be “significantly persuasive”. M Findlay and J Grix, “Challenging forensic evidence” (2003) 14 Current Issues in Criminal Justice 269 at 273. It appears to offer a degree of certainty that is often missing from a criminal trial. It also has the cache of being the topic of the moment on popular television.
This paper aims to address some of the issues that can arise when DNA evidence is put before the court at trial. I cover six key areas: · DNA science and technology; DNA science and technology Deoxyribonucleic acid (DNA) is found in all cells, except red blood cells. DNA is said by some to be unique to all but identical twins. However the fact, crucial for any understanding of DNA evidence, is that there is no scientific proof of such uniqueness.
“It is important to realise what a random match probability is not. It is not the chance that someone else is guilty or that someone else left the biological material at the crime scene. Likewise it is not the chance of the defendant being guilty or the chance that someone else in reality would have that same genotype. Rather, a random match probability is the estimated frequency at which a particular STR profile would be expected to occur in the population. This random match probability may also be thought of as the theoretical chance that if you sample one person at random from the population they will have the particular profile in question.” In New South Wales, the DAL biologists do not usually calculate their own match probabilities. They use an Excel spreadsheet and a commercially available program. They simply add in the figures, including the theta value (see below) and up pops the match probability. It is generally so high for a nine loci match that even allowing for an error range, figures well in excess of 1 billion are generated.
The standard report prepared by the NSW Department of Analytical Laboratories is usually brief and to the point: “I’m not into this detail stuff, I’m more concepty”, Donald Rumsfeld again. “The accused has the same profile as the DNA recovered from the crime scene sample. This profile is expected to occur in fewer than one in 10 billion individuals in the general population.” The explanatory note that accompanies the report contains these important qualifications: “The final statistical calculation … does not prove uniqueness, but provides strong support for the hypothesis (without taking other evidence into account) that the DNA from the evidence sample originates from the matched individuals. The profile frequency calculation does not apply to closely related individuals”. (Emphasis added). Other States follow a similar format. For example In South Australia a Report from Forensic Science South Australia might say: “The DNA profile obtained is approximately 990 million times more likely to match the DNA profile of the accused if he is the source of eh DNA rather than an unknown related male” Standard information relating to calculations of likelihood ratios, match probability and the type of Database used is attached.
The following areas require close scrutiny.
“Forensic scientists may become partisan. The very fact that the police seek their assistance may create a relationship between the police and the forensic scientists. And the adversarial character of proceedings tends to promote this process. Forensic scientists employed by the government may come to see their functions as helping the police. They may lose their impartiality”. R v Ward (1993) 96 Cr App R 1 at 51. An example can be found in R v Button, [2001] QCA 133. in which the forensic scientist looked only for evidence that would implicate the accused and missed crucial evidence pointing to the real culprit, because they did not do the tests. Justice Williams described the various failures in the case as resulting in “…a black day in the history of the administration of criminal justice in Queensland.” Deliberate failure to investigate is rare but we must be alert. The more likely cause of a failure to investigate alternatives is pressure of work and a focus on output rather than using the genuine forensic expertise of the analysts. The more procedures are automated the less the analyst has to do with analysing the samples themselves. See S Walsh, “Is the double helix a double edged sword?”, paper presented to UTS Speaks public lecture, May 2005. The quest for volume can mean only one exhibit or part of an exhibit is analysed. Sometimes as R v Button shows this is simply not good enough. When an expert or technician is cross-examined about what was tested it is sometimes prudent to find what was not analysed.
That while “normal handshakes” do not
appear to transfer DNA. This can be achieved under experimental conditions. The trial of Barnes Unreported NSWSC trial (Wollongong), February 2004, Buddin J. provides an example of secondary transfer. A young woman was found dead in a park in Dapto, her discarded clothing covering her naked body. The accused’s DNA was recovered from her bra. Other evidence pointing to Barnes’s involvement inn the death was equivocal. Evidence established that about an hour before her death the two had met outside a club. Both were drunk, and the accused in particular was in a jolly mood shaking hands with a number of complete strangers. The problem posed for the defence was, how did his DNA come to be on the bra strap of a women who when they met was wearing a vinyl coat and a singlet over her bra? The DAL analyst was dismissive of suggestions that spittle sweat or skin from Barnes’s hand had got onto either the victim or her jacket and then been transferred to the bra. The jury as evidenced by their not guilty verdict were more accepting of the possibility of secondary transfer!
In addition, it is assumed that:
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“Two different questions may be asked regarding evidence of a match between the defendant’s profile and the profile
obtained from a crime scene. First, what is the probability that the defendant’s DNA profile matches the crime scene sample profile, given that he or she is innocent? Second, what is the probability that the defendant is innocent given that his or her DNA profile matches the crime scene profile?” The first question assumes the innocence of the defendant and asks about the chances of getting a match; the second assumes that the defendant’s profile matches and asks about guilt or innocence. The
“prosecutor’s fallacy” consists of mistakenly giving the answer to the first question as the answer to the second”. Australian Law Reform Commission, Essentially yours: Protection of human genetic information in Australia, Report 96, 2003, Vol 2 at [44.29]. See also D Balding and P Donnelly, The prosecutor’s fallacy and DNA evidence (1994) Criminal Law Review 711, 716–717; R v Keir (2002) 127 A Crim R 198; and R v Wakefield [2004] NSWCCA 288. There is a clear danger of being overawed by statistics and falling into fallacious reasoning. “If your experiment needs statistics you ought to have done a better experiment”, Lord Rutherford quoted in NTJ Bailey, The mathematical approach to biology and medicine, 1967, Wiley & Sons, New York; “Statistics are like bikinis. What they reveal is suggestive, what they conceal is vital”; Aaron Levinstein; “Statistics mean never having to say you’re certain”, American Statistical Association T Shirt. An example comes from R v Keir. In evidence the DAL analyst said: (2002) 127 A Crim R 198 at [14]. “It is approximately 660,000 times more likely to obtain this particular DNA profile found in the bones if it comes from a child of CS and GB than from a child of a random mating in the Australian population”. The error was in the Crown, and later the trial judge, transposed this statement and directed the jury: Ibid at [16]. “There is a 660,000 times to one chance that those are the bones of G K (the daughter of CS and GB) as distinct from any other person”. Evaluating DNA evidence in context
“It is important to note that DNA will be only one tool in the police officer’s kit. They will still need to assemble a brief of evidence against the offender; DNA alone will not convict!” In R v Pantoja, (1996) 88 A Crim R 554 at 559, Hidden J agreeing. Justice Hunt made the same point. Although our understanding of DNA has advanced since 1996, the point still remains valid. A DNA link or match between the accused and a crime scene stain demonstrates only that the accused could be the offender. It does not establish that he was the offender.
“The courts have approached DNA evidence with caution. However that caution is naturally abating as experience with the use of such evidence has grown.” There have been strong statements in support of the proposition that DNA should be treated like fingerprint evidence. “The evidence was the subject of expert opinion and close scrutiny. The reliability and accuracy of the DNA analysis is beyond reproach. It appears much safer than eyewitness identification”. R v Rowe [2004] SASC 427 at [40] (SA CCA). “The use of DNA evidence appears to have reached a similar stage to fingerprint evidence in 1912. Like fingerprint evidence, Fingerprint evidence alone is good enough to convict: R v Parker [1912] VLR 152 (Vic CA); and in the High Court (1912) 14 CLR 681. it is of particular power, both to establish innocence and guilt.” R v Galli (2001) 127 A Crim R 493 at [106] per Spigelman CJ. “If the results indicate that it is at least 10 billion times more likely that the crime scene sample originated from the accused than from any other unrelated person selected at random from the population, then if the evidence is sound then beyond any doubt the accused is the offender. To paraphrase Anderson J in R v Shaheed [2002] 2 NZLR 377 at [207].” In most cases I have reviewed there is some other evidence, insufficient of itself to prove guilt, which the DNA evidence corroborates. Examples include: R v Gum [2007] SASC 311, where there were similarities in appearance between the accused and the alleged rapist; R v Fitzherbert [2000] QCA 255, where there was evidence of animosity and contact between the accused and the victim; R v Butler [2001] QCA 385 where the evidence was DNA and opportunity and R v Weetra [2004] SASC 337 where the accused lived nearby and stolen property was found near his home.
“The appellant sought to argue that because the DNA evidence was the only evidence of identification of the appellant, the conviction was somehow unsafe and unsatisfactory. The evidence was the subject of expert opinion. It was subjected to close scrutiny by the trial Judge who directed the jury that they must be satisfied beyond reasonable doubt as to the reliability and accuracy of the DNA analysis. It probably founded a safer basis for a conviction than the frailty often attending the evidence of a single eyewitness who gives evidence of identification of an offender. There is no substance in this ground.” (At [40]) I note that despite this view where DNA is the only evidence, the usual, but not exclusive practise, of the NSW Director of Public Prosecutions is to no-bill the matter. Cases where DNA is the only evidence are understandably rare, but are becoming more common as more and more serious offenders are placed on the offenders’ database. It was reported in The Advertiser of 28/8/2008 that South Australia had 41,161 profiles on its database, a 100% increase on a year before. Cold links are now being made, between crime scene stains and this database, with increasing frequency. Examinations of “cold cases exhibits” have turned up nuclear DNA from exhibits over 10 years old, see R v Stone (2004) 144 A Crim R 568. Stone pleaded guilty in 2004 to a 1990 murder. Sometimes cases are presented to court solely on the basis of this link. More often the link leads to further investigations and other evidence such as admissions, opportunity, identification or motive is presented. The DNA link then provides powerful corroboration of that other evidence.
· There is still so much we don’t know about DNA and statistics and population genetics, in he particularly areas of linkage between genes The best illustration is that some traits are not independent, for example, blonde hair and blue eyes. and interrelatedness. Illustrated by R v Bropho [2004] WADC 182. · The potential for human error. · The potential for contamination of samples. For an excellent review of why courts cannot be complacent about contamination, see K Edwards, “Ten things about DNA contamination that lawyers should know” (2005) 29 A Crim LJ 71. Most police forensic officers are well-trained professionals but not all exhibits are collected by trained professionals. Sometimes pressure of work or cost-cutting can lead to unacceptable shortcuts being taken. Examples of improper techniques that can lead to contamination of DNA samples include, improper bagging and storage of exhibits, for example, bundling them all in a bag or back of the car, transfer of DNA by fingerprint brushes, tweezers, or gloves which were used on more than one item. · Handling errors because of the conditions in which the DNA is kept or stored. It is surprising how many samples, numbers and barcodes do not match with numbers and barcodes recorded in notebooks or exhibit books. DNA profiles can be obtained from such small amounts of body tissue or fluid, it is often hard to avoid cross-contamination of samples. The most recent example arose in R v Murdoch in the NT Supreme Court (the Falconio case) where DNA from the chief of the laboratory doing the testing was found on a crime scene sample. · As we are dealing with statistical models a chance match simply cannot be excluded (and the possibility of a chance match increases if relatives or those from certain racial groups may be involved). · There is always a possibility of tampering with the crime scene. This is not to impugn the police or Laboratory staff. Other criminals could have left the sample and it would be naïve to assume that all police can resist the temptation to plant evidence. · The suspect’s sample could have arrived at the crime scene for a number of innocent reasons — secondary transfer or prior contact with the scene or exhibit. · DNA technology allows only for comparison of computer-generated profiles of the two samples of only a tiny fragment of DNA, There are over three billion pieces in the DNA code. The Profiler Plus system looks at only 10 segments of that total code. unlike fingerprints, where there is an actual physical comparison between the fingerprint found at the scene and that of the suspect or defendant. · There is danger that the statistical significance of a DNA match can be overstated. Some of the risks attaching to DNA evidence are only now becoming apparent. “The highly subjective nature of the mathematical process remains concealed behind the apparent certainty of a bald statistic”, Mathew Goode, “Observations on evidence of DNA frequency” (2002) 23 Adelaide Law Review 45 at 66–67. Examples include; the Eichelbaum-Scott report on DNA in New Zealand in 1999 The Rt Hon Sir Thomas Eichelbaum and Professor Sir John Scott, Report on DNA anomalies for The Hon Tony Ryall, New Zealand Minister for Justice, 30 November 1999, the inquiry in Victoria into how a female crime victim’s DNA was found in the Jaiyden Leskie murder, the more recent problem of contamination in the Gesah case The Age 22 July 2008 and 8 August 2008 and the number of what are called “unresolved pairs” often found when the data bases are searched for unexplained matches. Forensic DNA Evidence Interpretation, Buckleton, Triggs & Walsh CRC (USA) 2004 page 463. In 2005 Walsh and Buckleton reviewed Aboriginal DNA data bases for the National Institute of Forensic Science, in an unpublished report “on Duplicate detection” they noted that out of a sample group of 33,858 there were 1,575 matches, 206 occurred at 9 loci or greater. They explained these as being; coincidental matches between unrelated individuals, the same person giving more than one sample underran alias, close relatives matching or identical twins matching. The report also noted that in New Zealand a similar review had found 64 unresolved matches from a database of 50,000 people.
· they are the products of mathematical and scientific theory not concrete facts; · they do not purport to define the likelihood of guilt; · they should only be used to form a notion of the rarity of the genetic profile of the accused; and · the DNA evidence must be considered along with all the other evidence in the case relating to the issue of identification.
“The statistical evidence interpreting the significance of the DNA match is not evidence of the probability that the appellant was the source of the incriminating DNA. To so regard it would be to make an error. However, the statistical evidence interpreting the DNA match is expert evidence that the jury could use in deciding whether it was satisfied beyond reasonable doubt that the appellant was the source of the incriminating DNA. The statistical evidence is undeniably strong evidence pointing to a conclusion that the accused was the source of the incriminating DNA, but is not direct evidence of that fact. And, as is obvious, the statistical evidence must be considered in the light of other evidence in the case. It was for the jury to consider the evidence and to decide what significance and weight should be attached to the evidence. The jury were not obliged to act on the evidence. Nor should the jury allow any expert opinion put before them to be used as a substitute for their own satisfaction, to the appropriate degree of proof, of a matter required to be proved as part of the prosecution case. The proper approach to the issue of whether the incriminating DNA came from the appellant, and to the issue of guilt of the crime charged, was to treat the statistical evidence as evidence to be considered and weighed along with the other circumstantial evidence, not allowing it to displace or to overwhelm the consideration of all material evidence, but at the same time giving it such weight as the jury thought proper.” The case of R v S unreported, April 2006, NSWDC (Sydney), Norrish DCJ. illustrates the point. A rape victim described her attacker in detail and by name. That person’s DNA did not match the semen found. He was discharged. Later a cold link was made to “S” who had been in custody for unrelated and quite different offences. He was put on trial. He lived in the town where the rape occurred. Apart from his Aboriginality he did not match the description of the attacker. He did, however, have a close relative who not only matched the description but also had the same first name as the originally nominated suspect. That relative was not tested. The prosecution experts said that the probability of “S” providing the sample was astronomically high. 1:370 billion rounded down to 1:10 billion. It was still enormous even if a close relative couldn’t be excluded. Doubt was cast on those figures by the disparity between the descriptions, the untested relative, the acceptance by all experts that the profile could not be said to be unique, disputes between experts about Aboriginal Fst and the revelation of the unexplained matches on databases reviews. The jury had a doubt despite the statistical ‘certainty’ of the match probabilities given and “S” was acquitted. In no DNA case, should the question of guilt be approached strictly on the basis of mathematical calculation. R v Galli (2001) 127 A Crim R 493; and R v GK (2001) 125 A Crim R 315.
BIBLIOGRAPHY Forensic DNA Typing, JM Butler, 2nd Ed. Elsevier
(USA) 2005 What is a major problem with DNA evidence?Issues with using DNA testing in law enforcement: Errors
These issues include basic human error and human bias, linking innocent people to crimes, privacy rights, and a surge in racial disparities.
What are some disadvantages of DNA evidence?DNA evidence is only found in a small fraction of crime scenes.. Evidence such as confessions, murder weapons and other forensic evidence must supplement DNA evidence, as juries don't always base their verdicts upon DNA evidence alone.. What are the pros and cons of DNA evidence?Pros of DNA Evidence in Court. DNA Samples Can Exonerate the Wrongfully Imprisoned. ... . Greater Accuracy Than Fingerprinting. ... . Maintains Greater Integrity in Storage. ... . Can Prove Innocence When Other Evidence Might Not. ... . Potential Invasion of Privacy. ... . Not All Crime Scenes Have Recoverable Samples. ... . Hard to Prove How It Got There.. Why can a DNA sample not be a reliable source of evidence?DNA evidence is only as reliable as the procedures used to test it. If these procedures are sloppy, imprecise, or prioritize particular results over accuracy, then the so-called “DNA evidence” they produce cannot be a trustworthy basis for a conviction.
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