THE CASE OF THE WELDER'S DUST
The Evidence: In 1991, an 11-year-old girl was raped and murdered near Glennallen, Alaska. On her freshly laundered clothes investigators found flakes of glossy paint, tiny metal spheres and flakes, and red and blue polypropylene fibers. Charles Smithart, a local resident, had been spotted near the murder site, and the unusual interest he took in the case aroused suspicions, but investigators lacked evidence that directly linked him to the crime.
The Science: By subjecting the metal particles to the energy-dispersive X-ray spectroscopy detector on a scanning electron microscope, Palenik identified the spheres as iron and the flakes as brass. Iron dust takes globular form in only a few circumstances-such as when it is welded or subjected to grinding. Smithart engaged in welding in a shed behind his house, where he sometimes repaired bikes for neighborhood kids. The metal evidence, combined with strong similarities between the fibers on the girl and ones found on Smithart's vehicle and clothing, helped convict him at his 1993 trial. He appealed but died of lung cancer in December 2000, before his case was reheard.