Everyday Exposure to Toxic Pollutants; February 1998; Scientific American Magazine; by Ott, Roberts; 6 Page(s)

Imagine that a killer is on the loose, one who shoots his victims and flees. Police investigators would undoubtedly respond by visiting each crime scene and meticulously searching for clues. They would photograph the body, take fingerprints and question witnesses. An autopsy would recover the bullet for tests. The authorities could then use this information to establish exactly who was responsible.

But suppose the police took a different approach. What if they decided to start by examining all the guns that had recently been fired? Surely one of these weapons, they could argue, was involved. And they would be correct. They might even succeed in identifying the murderer--but not until after they had expended tremendous energy looking over a great number of firearms carried by law officers, soldiers and duck hunters. In a world of limited resources, they would probably run out of time and money before they came close to finding the culprit.