Optimizing Human Semen Stain Detection

Friday, October 28, 2011
Hall 1-2 (San Jose Convention Center)
Kelly Conroy , San Jose State University, San Jose, CA
Steven Lee, PhD , San Jose State University, San Jose, CA
Human semen fluorescence has been observed for many years and is currently used as a presumptive screening test in forensic laboratories.  The purpose of this project is to determine if a new set of fluorescence filters can be utilized with a forensic alternate light source (ALS) to improve the detection of semen stains.  To establish a baseline, a four year old positive control sample of semen deposited on a white tissue was examined under the Spectrum 9000, a forensic ALS, at six different discrete excitation filter settings.  The stain was then viewed through various long pass, short pass, and band pass filters covering a range of wavelengths as well as yellow and orange goggles (480 nm long pass, 545 nm long pass respectively).  Photographic documentation and visible qualitative evaluation of preliminary results indicate excitation wavelengths include 570 nm, whereas previous reports indicate semen excitation from 300-500 nm.  Fluorescence emission filters in the 510-590 nm range allow the stain to be easily detected by the eye.  Since fluorescence was observable at lower wavelengths that are blocked by the orange goggles commonly used in forensic laboratories, there is potential for capturing more of the visible fluorescence.  The results establish a baseline for a white substrate for the project, and the photos taken of the stain through the various filters will be analyzed using image analysis software to determine quantitatively if the unique discrete filters are indeed better than the methods currently employed in forensic labs for detecting semen stains.