Fingerprint Evidence

The evidentiary value of fingerprints

Fingerprints are the impressions of an intricate and unique pattern of ridges and whorls on the skin of human fingertips. These ridges form prior to birth and remain unchanged throughout an individual’s life, except variation in size or as a consequence of disease or injury. It is universally accepted that no two fingerprint patterns are identical nor do two people have the same pattern of ridges. In fact, the evidentiary value of fingerprints in identifying criminals is based on this unanimously accepted premise. Friction ridges or the swirled skin on the fingertips contain rows of sweat pores, and the sweat when mixed with other body oils and dirt produces fingerprints on smooth surfaces. Fingerprint experts use powders and chemicals to make such prints visible. The visibility of fingerprints depends on the surface from which they are lifted.

There are several factors adversely affecting the reliance of fingerprints in evidence. At times, the surface may not be suitable for retaining the minute traces of moisture in a form replicating the ridge features. In due course, the environment may also cause the print to deteriorate. However, computer enhancement techniques and laser technology are of great avail to fingerprint experts in retrieving identifiable prints from fragmented or smudged patterns. The FBI data bank has a collection of fingerprints as it is common that people may be fingerprinted in the event of an arrest or even when they begin certain occupations. In the latter case, it is as part of the background check of the applicant to rule out any criminal record.

However, it is not possible for the authorities to obtain fingerprint from any one with out a valid reason. The Fourth Amendment forbids the gathering of fingerprint evidence from “free persons” as it amounts to a significant interference with individual expectations of privacy. Hence law enforcement officials have to demonstrate that they have probable cause, or at least a genuine suspicion, to believe that the person committed a criminal offense and that the fingerprinting will establish or negate the person's connection to the offense.

Identification and matching of fingerprints

The determination of fingerprint evidence is done by experts who inspect and cross check the prints available from the crime scene with that of the accused or those fingerprints in the criminal data bank. This analysis is intuitive and hence subjective in nature as there are no uniformly accepted scientific accuracy standards. Different examiners and jurisdictions set their own standards, and the courts in the United States have largely left the definition of a match up of fingerprints to the experts themselves. Due to the prevailing notion that no two persons’ fingerprints are identical, a degree of infallibility is attached to fingerprint evidence that the authorities use to rush to conviction even without any other evidence. And many times, the state and federal judges do not usually question their evidentiary validity. Thus the actual determination of a match is based entirely on human inspection. Many experts consider this process to be a flawed science, especially with the emergence of DNA fingerprinting which is based on statistical calculation and hence more scientific and authentic.

Still, it is perplexing that many experts do not consider that a set of standards are necessary in the field of fingerprints. For instance, The International Association for Identification (IAI), which many experts look upon as the authority for fingerprint analysis certification, determined in 1973 that there is no need to require a set formula or “a predetermined number of characteristics to exist between two fingerprint impressions in order to establish positive identity.” On the other hand, the Scientific Working Group on Friction Ridge Analysis, Study, and Technology (SWGFAST), sets forth standards to assure quality fingerprint examination. Astonishingly, there is no requirement that these experts need to be certified. As such, various studies show that approximately 50% of the examiners who take the IAI test fail the exam, but are still permitted to work, thanks to the glaring lacuna in the field. Thus, there is no uniform definition of a match, and likewise, many states disagree on how many points of similarity are needed before declaring that there is a match. Internationally, many countries follow a definite point system to ensure a degree of accuracy. In Italy, for example, examiners say they have to have 16 or 17 points of similarity. In Brazil, it’s 30; in Sweden, it is seven points whereas in Australia, the requirement is 12. And it is bizarre to note that most examiners in the United States, including those at the FBI, don’t even use a point system.

The Mayfield episode in 2004 laid bare the fallibility of fingerprint evidence. In connection with a bag of explosive detonators found in Madrid, the U.S. officials booked Oregon lawyer Brandon Mayfield holding that his fingerprints matched a partial print found on the bag. The officials were pretty sure and called it “absolutely incontrovertible” and a “bingo match.” Mayfield was immediately taken into custody as a material witness. After some time the FBI admitted that it was wrong and the fingerprint actually belonged to Ouhnane Daoud, an Algerian.

The Daubert standards

Putting an end to the uncertainties prevailing in the area of admissibility of scientific evidence, which obviously includes fingerprints, the U.S. Supreme Court laid down certain standards in the 1993 decision in Daubert v. Merrill Dow Pharmaceuticals (113 S.Ct. 2786). In Daubert, the court laid down some definite parameters underpinning the veracity and evidentiary value of scientific evidence. The four-pronged test based on relevancy and reliability of scientific evidence includes questions of whether the technique employed can be (and has been) tested; has it been subjected to peer review and publication; what is the known or potential rate of error; what is the existence and maintenance of standards controlling the technique's operation and general acceptance in the scientific community.

Applying the Daubert standards, the court in the 2002 decision in United States vs. Llera Plaza, ruled that the use of fingerprint expert testimony should be limited. In this case, the court accepted the expert opinion.

The main allegation against fingerprinting is that unlike DNA evidence, it currently lacks any valid statistical foundation. “DNA profiling provides what is called a random match probability: the odds that the DNA of someone picked at random would match the profile in question.” Such a degree of statistical accuracy is not available in the case of fingerprints as per the present methodologies. The problem is acute in the hair splitting analysis of deceptively similar prints. The growing size of computer fingerprint databases makes this issue still more severe. As a database grows in size, the probability that a number of people will have strikingly similar prints also increases.

Conclusion

Even in the mercurial era of digital evidence and DNA profiling, fingerprint evidence is still considered as a reliable source. This is because of the inherent reliability of fingerprints. The main corrective required in the field is that there should be a sophisticated foolproof mechanism to prove the admissibility of fingerprints. Thus forensic scientists need to investigate the frequencies of different ridge characteristics and develop difficult proficiency tests that examine the capability of fingerprint experts to accurately differentiate between superficially similar prints, said Jennifer L. Mnookin in an article titled The Achilles' Heel of Fingerprints, which was written in the backdrop of the Mayfield affair.

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