Spattered blood intentionally hidden under layers of paint can be detected with a standard digital camera that’s been tweaked to record infrared light. The approach could become an important tool for cold-case investigators sizing up an old crime scene.
“We hope it gives law enforcement the ability to go on hunches,” says Glenn Porter, an expert in forensic photography at the University of Western Sydney in Australia. Blood is potentially powerful evidence, as it may harbor DNA that could allow a killer or victim to be identified.
Porter, formerly a forensic photographer with the Australian Federal Police, had heard of cases where investigators suspected that a crime had taken place in a now-remodeled house. So he and his colleagues decided to see if infrared photography might reveal blood hidden under paint. The researchers took a digital camera and swapped the light filters so the camera’s sensor would record only infrared light. With slightly longer wavelengths than visible light, infrared is better at penetrating layers of paint.