Crime scene investigation techniques are based on the application of scientific principles, and on what we know about the human body. Take fingerprint collection, for example. Biologists and scientists know that not only are everyone’s fingerprints different, with different patterns of raised ridges of skin, but those ridges are also constantly releasing perspiration. So, while you will certainly leave a fingerprint on an object if your fingers are dirty, you will still leave a fingerprint—an invisible one—even if your fingers aren’t dirty. It will be a fingerprint of perspiration, containing the natural oils from your skin. Investigators “dust” the prints by applying powder, which sticks to the perspiration and oils. Then they “lift” the prints with a clear adhesive tape. The result is an image that can be used in computer analysis.
There are numerous types of forensic techniques. When a liquid is splashed or splattered at a crime scene, investigators can study the splash and splatter patterns to establish what happened when the crime was being committed. Analyzing these patterns can help determine if someone is telling the truth about what actually happened. The splash and splatter patterns of blood at a crime scene can help police determine such things as whether someone was shot at close range or from a distance, from what angle, and if the person was moving or standing still. This all assists in the reconstruction of a crime, and can help to solve it.
Sometimes a body isn’t found until long after a crime has been committed. The skin and hair may have already decomposed, but there may be bones left, and bones can provide investigators with some amazing clues into who the person was. The shape and size of certain bones can help investigators determine if the person was male or female. The length and circumference of long bones (the ones in the arms and legs) can help approximate the individual’s height. One long bone is enough to provide an estimate of height, and if that bone happens to be the femur (the thigh bone), which is the longest bone in the human body, the estimate will be quite accurate.