Meanwhile, the techniques for retracing the evolution of a murder are getting ever more refined. Take soil samples. As bodies decompose, they leak five fatty acids into the ground beneath them. Each day after death, the various profiles of these acids will vary. Analysis of them can reveal the time of death, as well as pinpoint exactly how long any given body has been lying in a particular place. The soil can also reveal the presence of a corpse, even if the body itself has been removed or destroyed. The ''stain'' left by a body's volatile acids, which also suppresses plant life around it, can last for up to two years, leaving a kind of phantom fingerprint in the earth. Thus, soil, like maggots, becomes an ''information bomb,'' and the dead can be reconstructed (if not resurrected) long after they have disappeared physically.
