Science in the courtroom
‘‘I think we are vulnerable,’’ says Criminal Bar Association president Len Andersen. ‘‘I think it was a bit of a shock to discover that things like fingerprints are not as reliable as we thought.’’
Defence lawyers need more education about the weaknesses of forensic sciences, to ensure evidence does not go unchallenged in court, he says. But it’s hard to get a second opinion in New Zealand, given most forensic experts work for the police, via ESR.
Judges, not scientists, decide whether forensic evidence should be admitted in court. And judges rely on precedent, so even discredited science such as bitemarks continues to be admitted.
In her address to the 2016 Forensic Science Society symposium, Supreme Court Justice Susan Glazebrook said ‘‘it is important not to accept without question a type of evidence just because it’s always been accepted as reliable. Forensic scientists and the courts must keep abreast of changes in science and the development of new methods.’’
Since 2011, about 100 New Zealand judges have attended a two-day Understanding Forensic Evidence programme to help them assess the strengths and weaknesses of forensic evidence.
Deputy Solicitor-General Brendan Horsley says prosecutors are also expected to follow forensic developments and not present ‘‘shonky science’’.
However, he could not say if Crown Law had distributed the PCAST report (sidebar, right), or if its findings prompted any specific advice to prosecutors.
Forensic scientist Anna Sandiford thinks it’s unfair to expect courts to decide the validity of complex medicine and science.
Andersen believes the scientific evidence admitted in the trial of Mark Lundy – which had never before been used in a criminal case – overstepped the mark (see sidebar, below left).
‘‘Personally, I think the test allowed too much evidence in. The courts have to be a bit cautious in terms of stuff that is new, but on the other hand not rejecting scientific evidence.’’
In her 2016 speech, Glazebrook laid the blame for much of the forensics controversy on unrealistic expectations of science. ‘‘The more the myth that science deals in certainties is dispelled, the less the risk of science being misunderstood or misapplied by fact finders.’’
Sandiford agrees. ‘‘Courts and the media like scientists to be working in black and white and we don’t work in black and white, we work in shades of grey. It’s just a question of how grey it is.’’ Identifying or excluding individuals by analysing samples containing DNA from several people is ‘‘inherently difficult’’ and the conclusions of human examiners ‘‘varied wildly’’. New software automating that process, such as ESR’s STRmix, has been proved reliable for a three-person mixture in which the person of interest makes up at least 20 per cent of the intact DNA.
Bitemark analysis is ‘‘far from meeting the scientific standards for foundational validity’’, with doubt as to whether examiners can even reliably identify whether a bite is human.
While studies show fingerprint science is valid, it is not infallible. An FBI study suggested a match could be incorrect in 1 in 306 cases.
Analysis links ammunition to the gun that fired it by matching ‘‘tool marks’’ on spent shells. Current evidence ‘‘falls short of the scientific criteria for foundational validity’’, with the wrong gun identified in up to 1 in 46 cases.
Claims that shoeprints could be linked to an individual shoe, based on identifying marks on the sole, were ‘‘unsupported by any meaningful evidence’’.
A 2002 FBI study found that, in 9 of 80 cases (11 per cent) where hairs were deemed microscopically indistinguishable, DNA analysis showed they came from different individuals.