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The Science of Deduction

Sir Arthur Conan Doyle’s legendary character, world’s first consulting detective, Sherlock Holmes, was clearly a pioneer in the field of modern forensic investigation. Holmes’ scientific way of carrying out his investigations in a world where crime-solving was heavily dependent on guesses and coincidence, had revolutionized the field of criminal investigation. But of course, we are well aware of the science of deduction. However, what many remain oblivious to, is the role our little friends play in catching our man red-handed.

The death of an individual is followed by beginning of new life for the billions of microbes they carry with them. Unchecked by the immune system, they begin to proliferate and subsequently break down one’s body. Geneticist Jessica Metcalf of the University of Colorado, Boulder, hopes the macabre procession could provide a microbial clock that can help investigators tell the time of death more precisely than they can with recent methods, which depends on body temperature, rigor mortis, and insects.

Early in the decay, for instance, bacteria from the Moraxellaceae family and the genus Acinetobacter begin gorging on dying human cells. Moreover after, the Rhizobiaceae family, often involved in breaking down nitrogen sources, takes over. The gases produced by these bacteria cause the body to inflate and eventually rupture, giving oxygen a way and giving aerobic species the upper hand. Microscopic worms also start to multiply, probably feasting on the bacterial biomass now covering the corpse.

Metcalf first proced that she could depend on microbes, combined with a statistical model, to pinpoint the time of death of mice to within 3 days, even weeks after death. Her team, then collected samples from bodies at a specialized morgue or a so-called body farm, where the cadavers are displayed for forensic scientists to study and carry out their research. In a paper published in Science (8 January, p. 158), they reported that, once again, the pattern of growth of the microorganisms had been forseeable enough to set the clock. “Over 25 days our error rate is about 2 to 4 days,” said by Rob Knight of the University of California, San Diego, who is collaborating with Metcalf.

In a large new project, the researchers will expose 36 bodies, three at each of three different body farms, in all four seasons to help them further calibrate their clock and tell them how it is affected by the environment. So now that we know the true potential of our little detectives, criminals better watch their step, lest they wish to get busted. For “the game is on.”

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