FIRING bullets at blood-filled filter cartridges from a kidney dialysis machine might seem like mindless destruction, but it could give forensics investigators vital clues. The cartridges鈥� microstructure seems to accurately reproduce the effects of shooting at real flesh, and one expert reckons this could help detectives model patterns of spilt blood at scenes of shootings.
Interpreting blood 鈥渟patter鈥� at a crime scene is central to reconstructing what happened, but stand-ins for human flesh do not mimic the effects of shooting a real live body particularly well. To reproduce various spatter patterns, investigators normally soak a sponge in blood and shoot at it. But this is a poor model because the body doesn鈥檛 contain many reservoirs of pooled blood. Unless a bullet hits an area such as an open wound or a main artery, then spatter will actually be minimal, says Peter De Forest, a forensics expert at John Jay College of Criminal Justice in New York.
Forensic scientists disagree over whether to expect blood spatter from gunshot wounds. But De Forest says he has been involved in cases where forensics experts have interpreted a spatter pattern as due to a bullet wound, when it could easily have come from coughed-up blood, say. And such interpretations have been crucial in deciding the outcome of some gun crime cases, he says.
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What is needed is a better way to mimic a bullet hitting flesh. De Forest and his colleagues think they have found a more realistic model after a doctor told them that the cartridges from kidney dialysis machines are specifically designed to mimic capillaries. They contain bundles of hollow cellulose acetate fibres, which are each just 10 micrometres in diameter. Blood flows through these fibres and offloads waste products into a fluid in between the fibres.
One of De Forest鈥檚 colleagues, Peter Diaczuk, has shot at cartridges filled with his own blood. As they suspected, the initial shot produces virtually no blood spatter on pieces of paper mounted about 20 centimetres in front and behind the cartridge, he told a forensic sciences conference in Chicago. De Forest believes this more closely matches real gunshot wounds. A second shot to the same spot after blood has pooled produces copious spatter 鈥� also much more like what really happens.
Adrian Emes of Britain鈥檚 Forensic Science Service in London says the model could be a useful research tool. But he believes it will always be hard to predict when to expect spatter, because of complications such as hair and clothing. 鈥淚t is extremely difficult to simulate a specific circumstance,鈥� he says.