profile, they use electrophoresis (a blood-soaked piece of cotton placed in gelatin on a slide and submitted to electric current). In 1925, another blood-related discovery important to criminal investigation was made.? Around 80 percent of the human population were found to be "secretors," which means that the specific types of antigens, proteins, antibodies, and enzyme characteristic of their blood can be found in other bodily fluids and tissues.? In the case of a secretor, investigators can tell the blood type by examining the saliva, teardrops, skin tissue, urine, or semen. In a rape case, for example, where the perpetrator is a secretor, potential suspects can be narrowed down through blood type analysis. These days, thanks to discoveries in 1985, DNA technology has replaced the tests for specific enzymes and proteins.? It's more accurate to match DNA from a blood sample at a crime scene to a source than to draw up an entire blood profile. Yet blood at a crime scene can offer even more clues than gender and type.? Aside from the mere presence of blood, the different ways that blood lands on a surface has given rise to a forensic subspecialty known as blood-pattern analysis, or BPA.? Let's hear about that from one of the experts.