Fingerprint identification is one of the most commonly used methods by which law enforcement officials link criminals with crime scenes. Because every human has a unique fingerprint, forensic scientists can use the ridge detail found in latent fingerprints to place suspects at crime scenes. The ridge detail will show arches, loops and whorls that are unique to every individual.
The process of fingerprint analysis for the purpose of identifying criminals is often called Ridgeology, a term coined by a late 1950’s scientist.
Ridgeology: Types of Prints
It is possible to find three different types of fingerprints to use as evidence. The first is called “plastic”, and these types of prints are found in soft, malleable material – such as wax – and the fingerprint can be found on the surface. The second is called “visible”, and these are made when someone touches a viscous substance – such as oil or grease – and then touches a hard surface, leaving a visible fingerprint. The third – and most common – form of fingerprint is that which is made on a flat, hard surface and must be dusted before the fingerprint can be visible to the naked eye.
When law enforcement professionals locate a print or multiple prints at a crime scene, they are able to those prints to the ones stored on various law enforcement databases, such as the FBI’s NCIC classification system. The fingerprints will be photographed and then scanned into the database for comparison with other prints that are on file.
Ridgeology: Point System
Fingerprints are compared on a point-by-point basis, which means that even partial prints can be used to identify a criminal. In the United States, fingerprints must be matched based on twelve points of ridge detail in order to be admissible in court.
Latent prints are discoverable because of the chemical make-up of a fingerprint. Our skin secretes certain oils, along with perspiration, that is left on surfaces that we touch. The oil surrounding the ridges in our prints leaves a mark on the surface. Law enforcement professionals use powder to brush against surfaces at a crime scene, which will bring out the latent fingerprints. They use different colors of dusting powder – usually a color that contrasts with the color of the surface they are dusting – as well as fluorescent powder that works on multi-colored surfaces.
Once a print – or group of prints – has been located on a surface, the police must lift the print from the surface. There are several methods of lifting fingerprints, and the one chosen depends on the circumstances of the crime scene. They can lift the prints using rubber lifters or cellophane tape, whichever they feel will work best.
Ridgeology: Other Methods
In the last decade or so, forensic specialists have found other ways to discover and lift prints which were not available before. It is now possible to lift fingerprints that are more than twenty-five years old, which is valuable in cold cases where new leads have surfaced. Ninhydrin Spray, Silver Nitrate and Superglue Fuming are three of the most common modern techniques.
Ridgeology: Fingerprints Tell Other Stories
Fingerprints are only good for comparison when there are prints in the system with which to compare them. People who have never been arrested before, or who have never held a job where fingerprinting was standard, might not have any fingerprints on file.
In this case, police might not be able to find a suspect, but they can tell other things about a criminal from his or her fingerprints. First, the size might tell law enforcement whether the criminal is a male or female. Fingerprints left high on a wall can suggest height, and calluses in the fingerprints might suggest a musician or a construction worker.
Although these fingerprint inferences are not forensic evidence, and cannot be used in a trial or an arrest, they can help to set detectives on the proper path.