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Anna Valenn, Le Blog |
At the beginning, Sue Black’s forensic work centred around identifying victims. A successful identification often helps to define a crime, and makes a criminal investigation possible. But the investigation of a crime is about much more than who’s been on the receiving end. At its heart it’s about who perpetrated the act. That’s been at the core of crime fiction since the origins of the genre in the nineteenth century. Good scientists, like good detectives, develop new techniques to overcome particular problems. If these techniques are successful they can be applied to other similar cases. For Sue Black the blazing of new trails has always been a driving force. Wherever she can, she is determined to extend the range and scope of forensic anthropology. In recent years she has spent less time working out the identities of victims than she has on nailing the victimisers.
Nick Marsh, Head of Photography for the Metropolitan Police, worked alongside Sue in Kosovo, where they became friends as well as professional confidants. After he returned to the UK, he was confronted photographic unit. A 14-year-old girl had come to the police alleging that her father was abusing her at night. She had told her mother, who hadn’t believed her. The girl knew she needed evidence. Because she was tech-savvy, she knew that a webcam would switch to recording infrared light when it is dark. The girl set up her camera, pointed it towards her bed and clicked ‘record’.
She brought the resulting video to the police. The seemingly intractable problem Nick Marsh faced was that he could see there had been abuse. But because the camera had a very narrow view, the face of the perpetrator remained out of shot. Without a face or other obvious identifying marks, the video wouldn’t be enough to convict the father.
And so Nick turned to the one person he suspected might be able to help. When she viewed the video, Sue said, ‘It was one of the spookiest things that I’ve ever seen. I felt the hair go up on the back of my neck. At about 4.15 in the morning a pair of legs came into the shot of the camera and stood there. You can see where she is lying on the bed. She is wearing her pyjamas and it is her buttock region that we can see. And he just stands there – and I know it’s a ‘he’ because of the very, very hairy legs – and then very slowly extends his forearm, puts his hand underneath the covers.’
Like Nick, Sue’s first thought was that it would be impossible to identify the abuser. But she looked more closely at the footage and noticed that the infrared light had revealed the perpetrator’s deoxygenated blood, highlighting the superficial veins on his forearm. She already knew that superficial vein patterns differ widely. The further from the heart, the more clearly differentiated they are, so the veins on the hands and the forearms are the most individual ones that our bodies display. But to identify someone on the basis of these patterns would be a forensic first. At Sue’s suggestion, the father’s right arm was photographed. The veins matched perfectly with those of the man in the video.
When the case went to court, the defence questioned the admissibility of Sue’s evidence. The judge agreed that vein pattern analysis had no track record whatsoever. The jury was cleared out so the defence and prosecution could present their arguments on whether the evidence should be allowed or not. The judge asked Sue what she planned to say. By now she had realised that she should have photographed both the father’s arms to demonstrate how forearm veins differ, even on the same individual. In a bid to make her point, she asked the judge to turn his own hands over and look at the differences in his own veins. The judge asked her if her evidence proved beyond doubt that the perpetrator was the father. ‘No,’ she said candidly. ‘I haven’t done enough research to be sure that the pattern wouldn’t match anybody else in the world.’ The defence were desperate to get the evidence thrown out. It came down to the judge. Ultimately, the judge deemed the evidence to be admissable based on Sue’s anatomical experience concerning human variation, but it certainly helped that the defence expert was an image analyst rather than an anatomist, and that he irritated the judge by not turning his mobile phone off.
Sue testifed. The defence made their case. The girl was cross-examined. The jury deliberated and came back with a verdict that Sue had not been expecting: not guilty. Worried that she had over-stepped the mark, Sue asked the prosecution barrister to check with the jury whether the science had seemed at fault to them.
If it had, vein pattern analysis as a forensic technique would have to be modified or abandoned. The verdict from the jury was that it wasn’t the science that was the issue. That had made sense to them. They’d gone with ‘not guilty’ not because they didn’t
Forensics : The Anatomy of Crime by Val McDermid / Scènes de crime. 200 ans d'histoires et de sciences criminelles traduit de l'anglais (Écosse) par Omblage pour les éditions Les Arènes - Un traité de sciences d'investigation. Des topos clairs, illustrés par des tas d'histoires incroyables et vraies, et le tout écrit par une talentueuse auteure de polars. C'est passionnant.
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| and a firm reminder that truth is stranger than fiction |
Our fingerprints are part of us from before birth; they first appear in the tenth week of pregnancy, when the foetus measures only 8 cm. As one of the three layers of tissue that make up the foetus’s skin – the basal layer – starts to grow at faster rate than the other two, ridges form to relieve the resulting stresses, ‘like the buckling of land masses under compression’. If your finger pads were flat, the pressure on the skin would be equal and the ridges would be parallel. But because finger pads slope, ridges form along lines of equal stress, most usually in concentric circles. Ridge patterns also appear across the palms of our hands and on the bottoms of our feet. Other primates have them, too, and evolutionary biologists believe there are good reasons for them. They help our skin to stretch and deform, protecting it from damage; they create valleys down which sweat can escape, reducing slipperiness when we hold things; and they give us more contact (and hence grip) with rough surfaces like tree bark. When we touch a surface with a finger, the ridges leave their unique pattern on it. Even the prints of identical twins differ. In all the years that fingerprinting has been practised, no one has yet found two identical clear and complete prints belonging to two different fingers.