BioEd Online

British police have a new ally to help them with murder enquiries - dead pigs. The cadavers are being left at select locations around London in a bid to discover how rapidly bodies decompose when left to rot.

Forensic scientists have long used the bodies of pigs or other animals to simulate the changes occurring in a cadavar over time, in order to help police to work out how long a corpse has been lying undiscovered. The University of Tennessee, for example, has a forensic anthropology facility that famously hosts the 'body farm', which uses corpses in such research.

But the exact process of decomposition varies from place to place, thanks to the weather and the local bug population. So Zoe Adams, a forensic entomologist at the Natural History Museum in London, has expanded the work to London's streets and vacant offices to help police in the city. "We need to do experiments to get local information on each area. There's a variation between what would happen in Scotland and in London, for example," she says.

She hopes to work out how quickly the dead pig bodies in her study are colonized by blowflies. This could potentially be used to calculate a date of death even when the body has been lying around for weeks, Adams told the British Association Festival of Science in Exeter, UK, on 10 September. This would allow police to focus their investigation on a specific time window. "It will save police time, money and effort," she says.

On the fly

Current methods for evaluating the time of death - such as looking at rigor mortis, loss of body heat, and pooling of blood inside the body - are useful only for the first two or three days after death, Adams says. But the blowflies that lay their eggs on the cadaver are around for much longer, and show a characteristic progression through their life cycle.

A body crawling with adult flies, for instance, is likely to have been lying around longer than one infested with maggots. In cold conditions, eggs hatch out more slowly, and subsequent development is sluggish.

Adams is now busily depositing dead piglets in and around London - in woodlands, open pastures, inside deserted offices and on rooftops. She has studied six so far, with another three planned. Her recruits are drawn from the many piglets on farms who are accidentally killed when their mothers roll over on top of them.

The exact study locations are being kept secret because Adams doesn't want anyone to disturb her experiments. The pigs have all been placed on private land, and she has taken pains to get permission to use indoor locations too, such as deserted office space. "We found it difficult to find sites where we could leave our pigs to rot," she says.

Adams presented one of her piglets at the festival (thankfully in a plastic bag), saying that it had had more than 2,000 adult blowflies on it after 16 days at room temperature in an office in June. It was a similar story for a pig left indoors in December. But one left on a rooftop in winter was covered in eggs and yet still looked fresh after 27 days, she reported.

Entomologists had originally feared that flies might have more trouble finding bodies left indoors, making this kind of dating more difficult. "Flies will find a body within hours - they're very efficient," says Adams. "It was reassuring."