The American criminal justice system relies on the knowledge and equipment of many sciences and skills. Forensic evidence has become one of the strongest weapons for the successful prosecution of the criminal offenders. Some scientific theories and tests are so widely accepted and verified that they are virtually beyond criticism. The theory that each person’s fingerprints are unique, for example, has universal acceptance.
Historians believe that the Chinese used thumbnails to sign important documents before the birth of Christ. But it was not until 1870s that a British civil servant in India used fingerprints to record persons on pensions and prisoners in jail. Police in Argentina were reportedly the first law officers to use fingerprinting in 1891.
A criminal who carelessly leaves fingerprints at the scene of crime leaves latent fingerprints. Latent fingerprints taken from a crime scene can be compared with fingerprints on local, state and FBI files. The FBI has millions of fingerprints on file and receives more than 20,000 fingerprints a day from law enforcement agencies throughout the day.
An important question in the admissibility of scientific evidence is the theoretical and experimental basis of the scientific expert’s testimony. Courts traditionally use the Frye rule for the admissibility of scientific evidence.
In Frye v. United States, the U.S. courts of appeal refused to admit the results of a lie detector test given to a defendant in a murder trial. In rejecting the scientific basis for lie detector results, the court formulated what has become known as the general acceptance test:
Just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized. And while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs.
Latent fingerprints have been accepted as admissible scientific test. Fingerprints were first used as a method of identification in the late nineteenth century. Finger prints are different for every person, and they do not change with time. Various chemical substances are secreted form pores within the ridge found on fingertips, palms of the hand and soles of feet. Thus, when one touches an object with a fingertip, these chemicals are deposited in a pattern that reflects the ridge pattern on the fraction skin. First, it was observed that fingerprint could prove that a suspect was, not in fact, the criminal.
The oldest method of identifying fingerprints is iodine fuming. Iodine changes its state from solid to gas when heated. When the vapor comes in contact with the object, latent prints get enhanced and become visible. Magnetic powder and fluorescence are also used for fingerprint identification.
Fingerprints identification has evolved as a sound scientific technique accepted by courts and the scientific evidence. One of the first important cases that upheld the admissibility of fingerprint evidence as was the 1911 Illinois case of People v Jennings, in which the court noted, “The courts of this country do not appear to have had occasion to pass on the question”.
Fingerprint evidence is accepted by the court as the scientific evidence due to the unique nature of the fingerprints and it can assist in identifying the criminal and differentiate the suspect from the criminal. The techniques of fingerprint identification like magnetic powder are considered by court the admissible evidence.
Bridges, B. (1946, March). No duplicate fingerprints. Finger Print Magazine , pp. 5-6.
Cole, S. (2001). Suspect Identities: A History of Fingerprinting and Criminal Identification. Harvard University Press.
Frye v. U.S, 293 F (D.C. Cir 1923).
People v. Jennings, 252 Ill. 534 (1077 1911).
Wertheim, P. (2000, September/October). Scientific comparison and identification of fingerprint evidence. The Print , 16 (5).