Invisible Clues

Lives often hang on Palenik's precise identification of a fiber or fleck of metal. In his workday, there's no room for error.

By Gordon Grice Posted 09.27.2002 at 6:13 pm 0 Comments

THE CASE OF THE SPRAY PAINT SPHERES

The Evidence: About a decade ago, Brooker T. Hillery, a California man serving a life sentence for the murder of a 16-year-old girl in the 1960s, was granted a retrial. Seeking more substantial evidence than the tire- and footprints upon which Hillery had been convicted, investigators reexamined items belonging to both suspect and victim, and discovered on them tiny green football-shaped spheres. The spheres were apparently droplets of spray paint that had fallen from the cotton liner of Hillery's car (left, top), clung to him, and rubbed off everywhere he went, but a jury would require absolute proof that they shared a common origin.

The Science: Using a polarized light microscope, Palenik and local investigators confirmed that the spheres were each wrapped around a cotton fiber (left, bottom). Next, electron probe microanalysis revealed a composition of titanium, lead, and iron. Infrared microspectrophotometry showed that the paint base was an alkyd enamel, and the infrared spectrum identified the pigment as Prussian blue. Each sphere, whether from victim or suspect, possessed identical characteristics. Hillery lost his appeal and remained in jail.