Fact and Fiction About How Fingerprints Solve Crimes
When the average person thinks about how fingerprints solve crimes, they probably have an image in their mind of a Sherlock Holmes-type character with a deer slayer cap and magnifying glass snooping around a crime scene. The detective finds a promising fingerprint, examines it closely, and says Aha!. They have discovered the perpetrator, and the crime is solved on the spot. The reality of using fingerprint identification to solve crimes is much more complex and work-intensive.
Crime scene investigators spend many hours attempting to locate fingerprint markings or latents at a crime scene. Most are useless or too muddled to be of any real investigative value. Many crime scene prints belong to someone other than the perp, requiring the fingerprinting of anyone who regularly enters or uses the crime scene area.
Imprints that seem promising are dusted and lifted onto special tape or slides. They are then manually examined by an expert, who scores various unique identification points. The combined score of those key identifiers is converted into a unique number string that is different for everyone on the planet. If the suspect is unknown, a computer compares that score against the massive databases maintained by the FBI and other law enforcement agencies. If there is a known suspect, the process is easier, because the score is simply compared to the existing fingerprint file of the subject in question.
Fans of CSI and other TV detective shows often believe that police usually recover usable fingerprint latents at every crime scene. Thats far from true. The majority of physical surfaces do not retain usable latent prints, being too rough or irregular to bear an imprint with enough identifying features. Unfortunately, this belief is known among prosecutors as the CSI Effect, where trial juries are so convinced that forensic scientists are always able to find physical evidence that they will not convict a criminal if no such evidence is presented to them. Its particularly common with firearms, which rarely have a print friendly surface on their handles, so many believe that a criminal has not touched a weapon if their fingerprints are not found on it.
Fingerprint technology has come a long way, and is part of the new age of biometric measurement that will undoubtedly help police detectives greatly in their efforts to identify criminal perpetrators. Yet it has its limitations, and myths will always confuse citizens unless they truly understand the science behind how fingerprints solve crimes.