Alternate Light Sources
Alternate light sources aren’t just for developing latent fingerprints in the crime lab with fluorescent dye stains. Alternate light sources are also extremely valuable when searching a crime scene for physical evidence (Figure 1).
Figure 1: The alternate light source is being used to enhance bloody shoe impressions at the crime scene.
In addition to aiding in the development of fingerprints, an ALS should also be used in search of trace evidence like hairs and fibers, blood, body fluids, and impressions on human skin. We will talk about the latter, impressions on human skin.
Alternate light sources come in many different shapes, sizes, brands and light intensities. They start with 1-Watt light kits for a few hundred dollars all the way up 500-Watts in the tens-of-thousands of dollars. The more expensive the unit, the higher the power, and more power equates to better results.
Every human body in a criminal death investigation should be processed with an ALS prior to removal from the crime scene. It is impossible to just look at a body and make a determination whether or not physical evidence exists.
On a summer afternoon, I was dispatched to a rooming house in downtown Jacksonville where a body had been discovered. The male victim, wearing pants and shoes but no shirt, was found lying face-up on his bed. There were no obvious signs of foul play, the door was locked from the inside and nothing appeared to have been disturbed or missing. He had been dead for a short time, so the body was in good condition.
Figure 2: The partial boot impression luminesced only at 505nm of light and was visible with orange goggles.
After photographing the victim and the one-room scene and completing the rough sketch, I began processing the victim’s body. The body appeared unremarkable under ambient lighting conditions. Next, I closed the windows and pulled the shades down to make it as dark as possible. Using a bright rechargeable flashlight, I examined the body, and nothing was found.
By the time I finished the examination with the flashlight, another crime scene detective had arrived at the scene with the alternate light source. At that time we were using the Polilight® made by Rofin which had a 500-Watt Xenon arc lamp. It contained ten quartz filters and the frequencies could be fine tuned.
I began the search of the body with the white light, again with the room darkened. Nothing. Wearing the appropriate barrier filter goggles, I then went to the UV light at 400 nm, and still nothing. I proceeded through 425nm, 450nm, 475nm, and 490nm, all with negative results. Still wearing the orange barrier filter goggles, I lit up the body under 505nm of light and a partial boot impression appeared on the victim’s left chest (Figure 2). The light revealed the suspect had been standing on his chest. The impression, in some kind of unknown powder, was photographed. After completing the photography, I continued through all of the remaining frequencies up to infrared, around 695nm and the impression was not visible.
The impression was a significant find in this case. It would have been very easy to check the body with a white light and determine nothing was there. It is incumbent on the crime scene detective to use each and every piece of equipment that is available to its fullest; otherwise crucial physical evidence will be overlooked.
Michael F. LaForte is a forensic consultant for Knox & Associates, LLC, a Jacksonville, Florida based forensic consulting company that specializes in firearms, ballistics, and crime scene reconstruction. He was a police officer/detective with the Jacksonville Sheriff’s Office for over 29 years having worked in patrol, and crime scene investigations. In addition to being a major case crime scene detective, he spent the last three years as the training coordinator for the agency’s crime scene unit. He has also provided crime scene training in Peru, and around the United States. He has testified as an expert witness in crime scene reconstruction in state courts in Florida. He has authored three books on crime scene processing and crime scene photography.