Visualizing old biological traces on different materials without using chemicals.

During the investigative process that typically follows a criminal act, it may prove necessary to work with and analyze evidence that is not recent but old. This could become necessary, for example, when a crime is discovered some time after it was committed or when a cold case is reopened. Due to this need, the present study focused on the detection and visualization of 2-year-old biological traces. To do so, an alternative light source and different filters were used. The optical behavior of 2-year-old samples of blood, semen, urine, saliva, and sweat located on 19 different materials was documented, analyzed, and compared with the optical behavior of the same samples when they were recent [1].