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CSI SA: The creepy-crawly cops

18 May 2015 - 02:00 By Shaun Smillie

What Lieutenant Melanie Pienaar stared at under her microscope made no sense. Pienaar is a forensic entomologist who helps to establish the time of death in police cases. Often the kind of insect discovered on a body and the level of decomposition indicate how and when the victim died.What Pienaar found on the body of eight-year-old Kiana Williams was the maggot of a fly that appeared to have been in the wrong place at the wrong time.The fly, Muscina stabulans, usually feeds on faeces, not decomposing tissue.At the police victim identification centre in Pretoria, Pienaar keeps maggots from crime scenes alive until they become adult flies, then identifies them under a microscope. Maggots killed at the crime scene are used to establish the time of death.Pienaar's mentor, retired forensic entomologist Dr Mervyn Mansell, agreed with her findings and was just as baffled. The Animal Research Council at Onderstepoort also concurred.Pienaar's maggots increasingly originate from the bodies of poached rhino."The IO (investigating officer) needs a timeline for when the rhino was killed, to determine if the suspects were in the area at that time," she said.Insects that feed on rhino carcasses differ from those that feed on human corpses. One is a large blow fly, Chrysomya marginalis, which rarely feeds on humans. When it does, the speed of decomposition caused by the large maggot throws out forensic examiners.Establishing a time of death usually also requires studying weather conditions. By establishing what stage of its lifecycle an insect is in, and working out how long it would take to reach that point, Pienaar can establish when the eggs were laid, which in most cases is shortly after death.The wet and cold Cape weather of June 2013, when Williams went missing, made establishing when she was killed difficult.Pienaar found the answer in a photograph of the crime scene. "The fly was attracted to the smell of faeces from the stab wound to her abdomen," said Pienaar. The cold weather allowed Muscina stabulans to become the dominant species on the body.Pienaar could then determine when Williams died - the day she disappeared. Knowing the time of death could help investigators find her attacker...

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