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.