The most important material that investigators can find a crime scene is blood. It tells them a great deal. Blood is both a biological and a physical material. That is it has biological properties but it also behaves as a liquid. Employing both of these characteristics can be of great benefit to investigators.
Blood typing and DNA are usually readily done on crime scene samples unless they are so degraded that this type of testing is not possible. That is not often the case. Blood type and DNA can exclude some people and point the finger directly at others.
Blood behaving as a liquid can reveal to investigators how the crime occurred. Did the blood simply leak from a wound or did it spray from an arterial injury? Was it spattered as the result of a gunshot or blows to the head from a baseball bat? Did the victim standstill, lie on the floor, or walk or run away after the injury? The blood splatter pattern can reveal what happened and often where the various players in the crime were at the time the blood was shed. This can support or refute suspect and witness statements.
Often a killer will attempt to clean up a crime scene and scrub away the victim’s blood hoping that there will be no evidence of the crime remaining. Most of you are familiar with Luminol which has been employed in such cases. When properly used it can reveal blood splatter patterns even after the scene has been cleaned and indeed will often show the swipes and scrubs left behind by the cleaning utensil. It is highly sensitive and will find blood in the parts per billion.
Using Luminol requires that the area be sprayed with Luminol solution and then the room must be darkened and viewed using UV light. This can sometimes be cumbersome, particularly when attempting to evaluate a scene during the daytime. The windows in the room must be covered and all sources of light must be blocked out to get the best effect.
Add to this the fact that many other substances such as bleach, coffee, and rust can interfere with Luminol testing. Luminol can also damage the blood so that DNA testing will be less accurate.
Now it seems that a camera has been developed that will do the work of Luminol. It apparently uses pulses of infrared light and then measures the light reflected back to the camera. It filters out unwanted light wavelengths and concentrates on those consistent with blood proteins.
This is a very clever tool and hopefully it will work out to be as useful as it seems to be.