Fingerprints are a reproduction of friction skin ridges found on the palm side of the fingers and thumbs. A visual inspection of friction skin reveals a series of lines corresponding to the hills (ridges) and valleys (grooves). It is the shape and form of the skin ridges that one sees as the black lines of an inked fingerprint impression. All fingerprints are divided into three classes on the basis of their general pattern: loops, whorls and arches. Approximately 65 % percent of the population has loops, 30 % has whorls, and about 5% has arches. These three classes form the basis for all ten-finger classification systems currently in use. Fingerprints are inherently unique. No two individuals on the planet have the same fingerprints. Fingerprints are as unique as DNA.
Fingerprints are used frequently in criminal cases to identify the defendant and connect the defendant to the crime.
Although it is virtually impossible to change one's fingerprints, there has been no lack of effort on the part of some criminals to obscure them. The most publicized case involved the notorious gangster John Dillinger, who attempted to destroy his own fingerprints by applying a corrosive acid to them. Prints taken at the morgue after he was shot to death, compared to fingerprints recorded at the time of a previous arrest, proved that his efforts had been fruitless.