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RESEARCH

THIS IDEA MUST DIE:

Forensic evidence is always irrefutable

Forensic science still has a long way to go to always make a watertight case, says Dr Ruth Morgan.

Interviews Becky Allen Illustrations Jason Ford

Forensic science’s reputation is on trial. In April this year, the FBI admitted its hair comparison unit had given flawed testimony in trials going back 20 years, including 33 cases where defendants were sentenced to death. And in the UK, in 2007, Barri White’s forensic-based conviction seven years earlier for killing his girlfriend, Rachel Manning, was quashed. White was cleared of the murder, after which police resumed their hunt and ultimately convicted Shahidul Ahmed for the murder in 2013.

These, and other such cases, have thrust forensic evidence into the spotlight. If the proliferation of TV crime dramas – from ‘NCIS’ to ‘Dexter’ – are to be believed, the forensic scientist is king (or queen). Theirs is the most damning evidence, the result of highly specialist crime scene analysis that always delivers incontrovertible facts.

But however complex a fictional crime drama might be, what happens at crime scenes, in laboratories and in courts is far more complex – and more nuanced. Investigators and juries need to stop believing that forensic evidence is always irrefutable. And forensic science needs to continue addressing both the validity and the interpretation of forensic evidence. We need a stronger evidence base: more robust science to underpin the techniques and interpretations of evidence that people rely on in court.

In the majority of cases in which forensic evidence is critical, forensic science offers valuable intelligence evidence. However, I’m aware of the damage forensic evidence can do when people believe it is always infallible.

In 2007, the evidence in the Rachel Manning case was re-examined. In the original trial the most crucial evidence concerned some metallic particles found on Manning’s skirt – and in a van belonging to Barri White’s friend, Keith Hyatt. A forensic expert said the particles were extremely rare and this helped put White and Hyatt in prison. But our research found that far from being rare, the particles in question were incredibly abundant. At least 4,000 of them are produced each time a disposable cigarette lighter is used – and they can stay on people’s clothing for more than 18 hours. It was enough to quash the conviction and open the way for the real killer to be found.

One participant left none of her DNA but did leave some DNA from her partner – even though he had never been in the lab

That’s what the UCL Centre for the Forensic Sciences, part of the Jill Dando Institute of Security and Crime Science, is all about. Much forensic science in the UK is about developing new technology and new ways of finding more information. Our aim is to understand how evidence behaves and how we interact with evidence in casework, so we can ensure that our interpretation of what forensic evidence means in a case is robust and is based on empirical evidence; that’s crucial to preventing miscarriages of justice.

As well as looking at old cases, we also do a lot of work on DNA transfer. Fifteen years ago, DNA technology meant you needed a reasonable amount of material to get a DNA profile. Today, you can generate profiles from trace amounts of DNA. That sensitivity is powerful, but it also raises issues for the interpretation of that evidence in a forensic context.

In one project we’ve been trying to understand how much DNA the regular – as opposed to the last – wearer leaves behind on a garment. It’s been assumed the major DNA profile would be from the last wearer, but our research shows it depends on the person.

Miscarriages of justice like the Manning case are terrible examples of how forensic evidence can be misinterpreted and presented as unequivocal when it is not. For all our advances in technology, we still lack the evidence base for a lot of what’s being looked at. Our research is providing that evidence base for the robust interpretation of what trace evidence means when it is found. And that’s why I believe that the idea that forensic evidence is always irrefutable must die.

Dr Ruth Morgan is director of the UCL Centre for Forensic Science

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