Police: Atomic Fingerprints

Summoned by a burglar alarm, San Francisco police sped to a liquor store’s freshly jimmied door. Loitering there was William R. Woodward, 30, a private detective with no previous criminal record. On the ground was a tire iron that had apparently come from his nearby car. The cops arrested Wood ward for attempted burglary. But there were no fingerprints on the tire iron, and Woodward stoutly denied the charge.How to build a case? Answer: “radiation fingerprints,” a new scientific crime detector that makes Sherlock Holmes look like Deputy Dawg.

Telltale evidence against Woodward was produced by neutron activation analysis (N.A.A.), which subjects specimens under study to irradiation with neutrons in a nuclear reactor. The fine details of the specimens’ chemical composition can then be deduced from the pattern of radiation they give off. So sensitive is the technique that it can detect a thimbleful of poison dissolved in ten tank cars of water.

In monitoring the most carefully planned alibis, N.A.A. can be as revealing as a photograph of the actual crime. N.A.A. can link suspects to incredibly small bits of physical evidence, such as the infinitesimal traces of gunpowder left on the hand of someone who has fired a gun. N.A.A. helped to win a Canadian murder conviction in 1959 by matching the accused’s hair with tiny hair samples found on the victim. The first such U.S. conviction occurred last winter in a New York federal court, which accepted N.A.A. evidence as proof that the soil found on a truck hauling illicit liquor matched the soil around a moonshiner’s still in Georgia.

In Woodward’s case, police technicians found the tire iron minutely flecked with paint—a few specks resembling the light blue of his car, a few matching the light brown of the jimmied door. But there was no sure proof that Woodward used the tire iron to jimmy the door. The specks were so tiny (as small as one one-hundredth of a milligram) that conventional chemical or spectroscopic analysis was useless. So the police turned to a radiochemical research team headed by Dr. Vincent P. Guinn of General Dynamics Corp.’s General Atomic Division in San Diego.

Guinn’s scientists simply irradiated samples of the various paints and projected the resulting radiation patterns on an oscilloscope screen. Components of the two blue and the two brown paint samples were so alike that no one could dispute their common origin. At Woodward’s trial last month, a General Atomic scientist testified that it was “99.98% certain” that the tire iron came from Woodward’s car, “99.999% certain” that it was used to jimmy the door. A jury quickly found Defendant Woodward guilty as charged. Before the advent of N.A.A. he would almost surely have gone free.