Comparison of Latent Print Detection using Semiconductor Laser and LED Light Sources with Three Chemical Reagents

A variety of light sources and reagents are available for the detection and identif ication of latent prints. This study was undertaken to explore the optimum light and f ilter combinations of laser and light-emitting diode (LED) light for use with indanedione and two new reagents, genipin and lawsone. The light sources utilized were Coherent TracER lasers operating at 460 nm, 532 nm, and 577 nm and the Rofin Polilight Flare Plus LED operating at 505 nm. Deliberate and randomly created latent prints were f irst examined utilizing the light sources alone and then again following treatment with the chemical reagents. Results indicated that treatment with indanedione–zinc chloride was the most effective at the excitation of latent prints. With the exception of the 577 nm laser and genipin, the two new reagents, genipin and lawsone, did not provide useful results under test conditions. Although the LED light source revealed a signif icant number of untreated impressions, the laser light source proved to be more sensitive at detecting untreated impressions, and the ridge clarity was frequently higher on the samples examined. Monochromatic sources (lasers) and broadband sources such as LEDs each exhibited the potential to detect evidence missed by the other.