Light Kit Is Lower-Cost Crime Fighter

Sally B. Patterson

It has been a little more than a hundred years since Scotland Yard bagged its first criminal by using fingerprints as evidence. The technology for lifting a print back then was elementary, my dear Watson. It involved dusting it with charcoal and lifting it with an adhesive. Nowadays, tunable light sources and fluorescence imaging have made the process a more exact science. However, the five-figure cost of the high-end forensic light sources has been prohibitive for smaller crime investigation units, and the alternative -- basically a high-intensity flashlight with a filter -- is insufficient for sophisticated detection.

A forensic light with a halogen lamp filtered to provide cold light illuminates a sample. The device enables the investigator to visualize even microscopic traces of evidence. Courtesy of Schott.

Now, Edward E. Hueske of the University of North Texas in Denton and William Walker of the Police Department in Bedford Texas have tested a device and accessories that they believe answer the need for a fully functional light kit with a low-four-figure price tag.

In an article in Southwestern Association of Forensic Scientists(Vol. 25, No. 1), they have reviewed the forensic kit from Schott of Auburn, N.Y. Based on the company's KL 2500 liquid crystal display cold light source, the system includes an integrated filter wheel, a flexible lightguide, blue and green excitation filters, red and yellow barrier filters and goggles, and a spot lens.

The illumination is produced by a 24-V, 250-W halogen reflector lamp whose aperture and bulb brightness are adjustable via stepless control knobs. The lightguide transmits the visible light from the lamp but not the heat that it generates.

The forensics specialists used the light source with different filter combinations and a variety of fluorescent dyes to examine both prepared samples and objects from criminal cases. Hueske said that the instrument worked effectively on most surfaces, including paper, plastics and metals, and even on crumpled foils. It can detect residues such as fingerprints, blood, semen and hair, as well as fiber samples and gunpowder particles.

The reviewers found that it allowed full visualization of prints that had been pretreated with fluorescent powders or dye stains, and they praised the convenience of the flip-up goggles that didn't have to be removed for viewing evidence in normal lighting. Although they did not test the system's remote control capability, they said that it would be helpful for extended usage. They suggested that a wider choice of filters would make the device even more flexible, and Schott representative Jeff Smith said that the company is looking into that.

The company says that the system is already in service as a light source for microscopy and that a cold light source is advantageous in both biological and forensic applications because it doesn't damage or destroy the specimen.

Law enforcement agencies in Germany and Romania are already us-ing the kit as a crime investigation tool, and it is being tested at Scotland Yard -- where fingerprinting got its start.