The Study of Fingerprints in Forensics
The science of gathering and examining fingerprints has been a critical part of law enforcement since the early 1900s. Fingerprinting technology allows law enforcement professionals to concretely tie a person to a given crime scene. The uniqueness of each person's fingerprints allows this. Therefore, the discovery of a print is admissible evidence in court cases and allows prosecutors to tie a suspect's whereabouts to any given location.
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Gathering Prints
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To study fingerprints, the prints first need to be gathered intact from a crime scene. Usually, the fingerprint is left on a surface that retains the oils from a person's finger. Investigators dust a light coating of a powder onto that surface. Ninhydrin, aluminum, magnesium and graphite are all examples of powders that are used for fingerprinting. Once the print is visible, it is documented through photography and the powdered print is placed on a piece of tape for further examination.
Analysis
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Fingerprinting experts analyze fingerprints by zeroing in on certain key characteristics of the print. First, they find the focal point, also called the core of the print. Characteristics such as the number of ridges or how the ridges divide are what make fingerprints unique. There are also three shapes looked for by analysts that identify unique fingerprints. Whorls, loops and arches all describe specific shapes seen in fingerprints. These shapes are looked at and compared to a suspect's samples to see if there is a match.
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Computer Analysis
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There are far more fingerprints that need to be analyzed than can be completed by human forensics experts. As a result, fingerprints are now most commonly examined by computers. The prints are fed into a computer that compares the print to the databases of prints on file. Several databases might be searched for fingerprint comparison, but often the Integrated Automated Fingerprint Information System (IAFIS) used by the FBI is the first database that investigators will run a search through.
Partial Prints
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One of the troubles often faced by forensic investigators is when they only find a portion of a print on a given surface. In these instances, the partial print is still fed into a computer. Then, a partial print algorithm of some kind will be used to try and find the mathematical likelihood that a given set of prints is a match. The difficulty of doing this depends on how much of the print was captured and what features were captured. If a core or delta is captured, for instance, it is much easier to prove a match than it is without.
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References
- Science Encyclopedia: Forensic Science - Fingerprints
- Explore Forensics: Fingerprints
- The National Association of Criminal Defense Lawyers; A Cautionary Note About Fingerprint Analysis and Reliance on Digital Technology; Michael Cherry; 2006
- American Judicature Society; How We Can Improve the Reliability of Fingerprint Identification; Michael Cherry, Edward Imwinkelried; 2006
- "Pattern Recognition"; Cedar; A Minutia-Based Partial Fingerprint Recognition System; Tsai-Yang Jea, V. Govindaraju; 2005
Resources
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