Why do judges keep letting bad science into criminal trials?
By - Posted on 22 July 2021
Relying on past decisions made by other courts 鈥� called "precedents" 鈥� is a handy shortcut for the UK legal systems and similar systems in the USA, Canada, Australia and New Zealand. It saves running the same arguments over and over again, it helps keep court decisions consistent over time, it reduces trial running-times, and helps lawyers advise their clients about how their case might be decided by a court. Precedent means that cases already decided by higher courts 鈥榖ind鈥� any subsequent cases heard in lower courts, or courts at the same level. So a decision of the Supreme Court must be adhered to in all similar subsequent cases in that system, unless the decision has been modified by parliament, or the lower court can successfully 鈥榙istinguish鈥� its current case from the decision in the precedent.
Unfortunately, this means that where a court allows poor quality evidence into a trial, such evidence is likely to be used again and again in subsequent cases. There is a further way to 鈥榞ame the system鈥� of precedent though, and some prosecutors use this for emerging or controversial forensic science techniques that are very convincing for juries but might have unproven or highly contentious scientific credentials. Here the prosecution is able to wait for a case where the defence is poor (underprepared, under-resourced, or incompetent) and will present the sub-standard forensic science evidence to the court in that case. Because the defence is underprepared, under-resourced or incompetent, the poor quality forensic science is not challenged; it is accepted by the court as evidence against the accused.
This means that in subsequent cases, even if the defence is stronger and starts asking good questions about the validity and reliability of that type of forensic evidence, the prosecution can say 鈥� hand on heart 鈥� 鈥榳ell this evidence has already been accepted in X number of cases, your Honour鈥欌��
This is a very persuasive argument for allowing the evidence into the current case, because鈥� . So even though the forensic evidence might be unreliable, invalid, poorly executed, or totally without scientific merit, the defence will be hard-pressed to get it excluded from the case against their client. Judges are far more likely to and admit the evidence.
Sound far-fetched? You might be surprised to learn that several important scientific bodies have repeatedly found that much of the 鈥榝orensic science鈥� we take for granted in not actually scientific. For instance in 2009 the :
鈥淸M]uch forensic evidence鈥攊ncluding, for example, bitemarks and firearm and toolmark identifications鈥攊s introduced in criminal trials without any meaningful scientific validation, determination of error rates, or reliability testing to explain the limits of the discipline.鈥� (at page 108)
And more recently the :
鈥溾�xpert witnesses have often overstated the probative value of their evidence, going far beyond what the relevant science can justify. Examiners have sometimes testified, for example, that their conclusions are 鈥�100 percent certain;鈥� or have 鈥渮ero,鈥� 鈥渆ssentially zero,鈥� or 鈥渘egligible,鈥� error rates. 鈥� such statements are not scientifically defensible鈥� (at page 3)
This has become a problem even with what judges and juries might consider to be 鈥榞old standard鈥� forensic science such
How can the prosecution get away with this? They have the advantage of being repeat players in the game of criminal law, whereas your average criminal has nowhere near the same collective experience and resources. Even with big budget cuts to the prosecution, police, , the prosecution remains THE repeat player, with an ever-replaceable cast of lawyers, police, laboratories, and expert witnesses on hand. In contrast, each accused person is little more than a one-shot player, unaware of and unable to control the behaviour of the prosecution over millions of cases and hundreds of years. The final piece of the puzzle is that judges are bound by precedent, :
鈥淭he problem for the defense is that every single court...has admitted this testimony鈥 reluctantly [admit the evidence] because of my confidence that any other decision will be rejected by the appellate courts, in light of precedents across the country, regardless of the findings I have made鈥� (at page 108 of the 2009 American report)
Cherry-picking cases to insert unreliable forensic science into the criminal law is an abuse of the system. So what is the solution? It isn鈥檛 to ban the use of scientific evidence in criminal trials, or even to ban the use of new, controversial or untested scientific evidence. The fact is, forensic science experts know things that we don鈥檛 know, and that鈥檚 makes them extremely useful in criminal trials because victims deserve justice, and the liberty of an accused person hangs in the balance. Nor is the problem solved by getting rid of our system of precedent, which has served us well for centuries. Rather, we need to make sure that the defence is properly equipped to hold the prosecution to account in every case, , and poor quality expert evidence is no longer allowed to slip through the cracks and into the criminal law.
Further analysis of this and other issues can be found in a co-authored article by Professor Donald Nicolson and Dr Wheate in the Juridical Review: 鈥楾he Young grandfather: a new approach to the reliability of expert evidence in Scottish criminal cases or business as usual?鈥� 2020 Jur. Rev. 111.