Forensic evidence and expertise in court | The Courtroom


Our job is not to help the police,
our job is not to be involved in the investigation. Our job is to prepare evidence for the court and that’s the expert witness
part of what we do. Sometimes our evidence will be heard in court
without us needing to appear there. Other times our evidence will be heard
and we will have to give an oral presentation as the expert witness in the courtroom. We use forensic experts in court to provide the results of their
examination of the physical evidence but examined in a structured way
using specialised knowledge which is likely to be beyond the realm
of the ordinary member of the jury, ordinary member of the public. So it is expert guidance for a jury
when needed, whatever the discipline may be,
whatever the type of physical evidence but ultimately it’s for the jury to accept or reject
the expert guidance that they are given. Whether it is a homicide case
involving analysis of the body or a case involving live people, the principle areas of forensic expert
evidence will be DNA analysis, blood analysis, which may
include toxicology, fingerprint analysis and
sometimes more esoteric areas which in recent cases have
included ear print analysis, for example, when a burglar
casing the joint put his ear up against the window
of a home that he wanted to enter, the question was: did he leave
a unique or a distinguishing mark which could rule out others? Blood pattern analysis is a very frequently
used tool in criminal forensic cases. An example would be
the killing of Damilola Taylor, the 10-year-old boy who died in
a Peckham stairwell over a decade ago. In his case, which went to trial twice
involving different defendants, all of them teenagers who
were charged with that crime, the analysis of a droplet of blood
on a trainer shoe found at the home of one of
the defendants some months later, became crucial to the case and
blood pattern analysts were essential to a jury understanding the nature of the case
that the prosecution were bringing to bear. And I have no doubt that
that evidence was very important in ultimately securing the conviction of two individuals
for the manslaughter of Damilola Taylor. Presentation tools used in court
by expert witnesses are obviously important because
an expert witness needs to settle a jury, to reassure them that the expert knows
precisely what they’re talking about and more importantly to distil the
essential features of the expert analysis without it becoming a postgraduate lecture
in physics, chemistry or biology, which is beyond barristers
and is beyond most juries. So the way you present is key. The way that you keep, maintain and
produce your background working notes can also be of fundamental importance. So any proposition that you make,
any conclusion that you reach must be backed up by original working notes, which are often called for and can be
examined in court by an opposing expert, not to suggest that there is an
unseemly battle between experts, but peer review of expert work
is part of the mechanism by which a court judges
whether this is true expertise that can be dealt with
within our adversarial system. Accuracy of evidence is really important and that accuracy has also got to reflect
on the experience of the individual as well, it’s not enough to stand up in court and say, “I’ve done 10,000 of these so I’m good.” You might have done 10,000 but
you might have done them really badly. So it’s important that at all times
everything we do is critically checked so that in Scotland we have
a two-pathologist rule so that we always work together,
so there is always a team but if we’re working on a case
in England and Wales, I might write the report and
I will pass it as a critical check to somebody else within my department. We are all here professionally certified
by the professional body, which is the Royal Anthropological Institute,
so we’ve gone through examinations that show that we do at least
have some level of expertise and knowledge and understanding. And so for us you accredit the expert
and then you take the evidence that that expert produces and you
pass it to somebody else and you say, “Be critical about it. Have I said
something that I can’t substantiate? Have I missed something out
that I should’ve said?” And that critical check is really important and every single one of our reports
before they pass out through the door here is critically checked. Before you write your statement of evidence, in other words summarising
everything you’ve done, it’s normally the end product of what goes on
at crime scenes and in the laboratory, the end product of the
forensic scientist’s work, but before you do that you
really make sure that you’ve got it as right as you possibly can and
you’ve done enough to make sure that you can conclude what you’re going to conclude, and that you’re not going out on a limb. I mean our quality systems require it
anyway, but you always do want for your work to be peer reviewed
or the main aspects of it, so you get your colleagues,
or really experienced colleague, to come and give you an
independent opinion of what they think are the specific aspects of your evidence. And then you write your statement,
you read it, you think about it, and then you may ask advice again. So really, in terms of preparing
what the court’s going to hear, a lot of that should have been done before
you ever release anything from the laboratory. And then after that you’ve only got to
worry about remembering what it was you did, what the case was about
and then just presenting it orally in as clear a way as you possibly can. The impact of DNA analysis since the
emergence of that science in the 1980s has of course been
enormous on criminal trials but the cases in which it’s been deployed
have shown, particularly in the early years, just how difficult it is to understand
by the layman or laywoman and how important it is to comprehend
the statistical analysis of DNA. Many people are familiar with what’s
known as ‘the prosecutor’s fallacy’ where the statistical evaluation of
DNA findings can be misinterpreted and, to put it simply, can be
made to look like empirical proof, empirical evidence of identification. But as scientists know,
that is beyond DNA analysis. When a scientist, who has conducted a
DNA analysis says to the jury that there is, what is commonly called,
‘a one in a billion match for DNA’, it usually has a
visible impact upon a jury. But again, scientists know that a
one in a billion match is not actually a match, it’s a one in a billion
statistical evaluation. But let’s take an example where there may be
family members involved in a case, that will immediately dilute whatever
statistical evaluation there is, and all the more so if
there are, for example, twins, twin brothers or sisters involved in a case. We all know the genes,
the blood pool, the DNA pool that we inherit
from other family members and where there are complications like that, although DNA has a
visible impact on juries, they require very careful guidance
on just how much use they can make of DNA in cases like that.

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