The use of an alternative light source to detect semen in clinical forensic medical practice

One of the primary aims of forensic examination in sexual offences is to detect and recover biological material that will link the offender with the complainant. One potentially valuable method by which trace biological evidence may be identified in other forensic settings is via the use of an Alternate Light Source (ALS).

The aim of this study was to determine whether or not there was any potential benefit in using an ALS as an adjunct in sexual assault examinations to aid the detection of forensically relevant areas on the body which are not identifiable on visual inspection for sampling. We present two case reports, which illustrate the potential value of using an ALS in clinical forensic medical practice as an adjunct in sexual assault examinations to detect potentially forensically useful areas of skin to sample for semen.

Prior to introducing the ALS into our clinical forensic medical practice, we undertook a number of simple laboratory studies to determine a protocol for its use. Semen is known to fluoresce using an ALS at a wavelength of 450 nm. Although we did not conduct a rigorous scientific evaluation of the technique, we evaluated the use of an ALS to detect semen on a range of inanimate surfaces as well as human skin. On all surfaces, visibility of fluorescence was increased by reduced distance of light source from the surface and increased concentration of semen on the surface, but was not noticeably affected by the angle at which the light source was held in relation to the surface.