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Forensic fingerprinting is the process of using fingerprints to prove that a specific person was present at a specific place or touched a specific object. This is usually done as a way of proving guilt or innocence in criminal cases, although it has limited uses outside this area. Humans have ridges on their fingers that are generally unique to an individual. As a result of the oil and sweat on a person’s hands, humans will leave fingerprints on practically everything they touch. Skilled forensic scientists can differentiate one person’s prints from another and then match the print to preexisting records to prove identity.
When a person touches a surface, small amounts of material are usually left behind. This material will conform to the ridges found on the hands and feet, since those are the areas that made the most contact with the surface. For a person skilled in forensic fingerprinting, this material is a key to the identity of the person that left it. The difficult part is that while nearly every person’s fingerprints are unique, most prints will vary each time they are made — it is also not unheard of for multiple people to have sections of ridges that are practically identical on their fingers. The angle at which the print was formed, the surface touched and the pressure applied all have huge effects on the structure and design of the print.
In order to sift through this, a person performing forensic fingerprinting will compare key points between prints to look for common factors. As a print is made, certain sections will look the same as other prints while some sections won’t. By comparing points on the finger that suffer the least distortion and those areas that match across prints, it is possible for forensic fingerprinting to determine a likely match.
There are four main types of fingerprints. An exemplar print is the term for a print that was specifically taken to be a fingerprint record. These are typically the best possible prints, as they are taken in a controlled environment using professional methods. Plastic prints are the other preferred type of print. These prints are perfectly preserved prints contained in three-dimensional form, such as an impression in clay or plaster.
The most common prints used in forensic fingerprinting are the two that are not so well-made. A patent print is a fingerprint that is visible to the naked eye. These prints are often made by touching a dirty or very clean reflective surface, such as a dusty car or mirror. Latent prints are invisible under normal conditions. These prints require special powder or lighting conditions to become visible.
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