Fingerprint Evidence in Criminal Cases

Fingerprint Evidence in Criminal Cases:  Fingerprint evidence, although not as high-profile as other high-tech crime-solving methods like DNA, is still very much used in criminal investigations and cases.  While the expert may say that “no two people can have the same fingerprints” cannot be validated, fingerprint evidence is generally considered to be highly reliable and is particularly accessible to juries.  

Matching Fingerprints:  Fingerprint evidence rests on two principles:  (1) A person’s “friction ridge pattern” don’t change over their lifetimes; and (2) No two people have the same pattern of friction ridges.  Even identical twins have different fingerprints.

The Government uses fingerprints to identify defendants by comparing prints found at a crime scene with prints already in police files.  Today the FBI has a collection of prints that number about 60 million.  People’s fingerprints can be on file for a variety of reasons.  For example, people may be fingerprinted when they are arrested or when they begin certain occupations.  

Fingerprint experts can disagree about how many “points” in common are needed to declare a match between two sets of fingerprints.  For example, some experts will declare a match based on only 12 points in common, whereas other experts may require up to 20 points in common before declaring a match.

How Fingerprints are Found:  friction ridges contain rows of sweat pores, and sweat mixed with body oils and dirt produces fingerprints on smooth surfaces.  Fingerprint experts use powder and chemicals to make such prints visible.  The visibility of a set of prints depends on the surface from which they are lifted; however, with the help of computer enhancement techniques that can extrapolate a complete pattern from a mere fragment, and laser technology that can read otherwise invisible markings, fingerprint experts increasingly can retrieve identifiable prints from most surfaces.

The age of a fingerprint is impossible to determine.  Therefore, defendants often try to explain that their fingerprints were found at crime scenes by testifying that they were at the scene and left the prints at a time other than the time of a crime.  

Marinaro Law, our attorney’s experienced with how to cross-examine experts regarding fingerprint evidence.  It is well documented that fingerprint analysis is not an exact science and often false positives result.  Call our office for representation should you have a case involving fingerprints.