Police officers, crime scene investigators and others in the justice system rely on forensic science techniques to ensure that the right people are punished for law violations and to keep people safe. Fingerprints are starting players in the criminal offense and defense lineup. They are so important to criminalistics that justice officers still use fingerprint systems over a hundred years after scientists developed them.
To understand why fingerprints are so crucial to forensic science, one first has to understand what a fingerprint is and how justice officers retrieve them. A fingerprint is a unique image produced when the folds, twists, and turns of the ridges on the pads of the fingers are scanned or pressed on paper after being pressed on ink. Every person in the world has distinct variations in their ridge folds, twists and turns, so a fingerprint image is like a little stamp that says "I was here," with no two people having the same ridge variations. Crime scene investigators usually gather these prints through physically lifting them with fingerprint powder and a sticky tape, but new technology also lets crime scene investigators take digital scans of fingerprints that are too fragile to lift.
Not every crime scene has DNA evidence that is useful to prosecuting or defending a case. Evan Sycamnias of Uplink states that, in these situations, fingerprints are one of the most important factors in crime solving because they may be the only means of identifying the people who were at a crime scene or who are involved in a crime. In some instances, criminalists may use fingerprints not only to identify criminals, but also to identify their victims and missing persons.
Proof and Reasonable Doubt
Fingerprints may not prove with 100 percent certainty that someone committed an offense. For example, if a crime scene investigator finds a man's fingerprint on a wine glass next to a dead woman in a hotel room, this just indicates that the man was in the room. It doesn't prove that the man took the woman's life. However, fingerprints greatly reduce the number of suspects that justice officials may need to consider, and they can establish or refute a suspect's alibi in order to create reasonable doubt.
Some fingerprints deteriorate over time as the environment wears them away, according to Quo Jure. The state of fingerprints thus may give investigators a clue as to when a crime occurred. This also helps when trying to determine who might have been able to commit the offense(s) in question.
Justice officers take great pains to keep records of as many fingerprints as possible. The Thin Blue Line reports that justice officers keep databases known as Automated Fingerprint Identification Systems (AFIS) that contain fingerprint images and information related to the person each print identifies. Law enforcement officers who have appropriate clearances access AFIS at varying points during their investigations to refine their suspect lists or identify individuals.