Fingerprints

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Note: This article is mainly based on a document entitled "Fingerprints" by the non-governmental organization "Forensic Experts and Jurists' Association"[1].

Definition

The surface of the human skin on the tips of the fingers, palms of the hands and soles of the feet, unlike the skin on most of the rest of the human body, is continuously corrugated with narrow ridges.

Fingerprint is an impression of the friction ridges of all or any part of the finger. In a wider use of the term, fingerprints are the traces of an impression from the friction ridges of any part of a human or other primate hand[2].

Why are fingerprints utilized?

Fingerprints (and other ‘friction skin’ patterns) are used as a means of identifying people, particularly in criminal justice systems worldwide. Fingerprint evidence has enjoyed widespread acceptance and use as a legal means of proving in the courts for many years.

This type of evidence plays a crucial role in criminal investigations, and the fingerprint examination (expertise) is the most applied investigative means in criminal matters.

A person’s fingerprints are unique and do not change during the course of their life. No two fingerprints have ever been found alike in many billions of comparisons. That’s why fingerprints can be used to quickly and efficiently confirm (or disprove) a person’s identity.

Fingermarks can be collected at a crime scene and have the potential to link a series of crimes together, or to place a suspect at the scene. Fingerprints play an equally important role in indentifying victims following a disaster such as a cyclone, earthquake, bombing or other attack[3].

When are fingerprints utilized?

Fingerprint identification is utilized at many levels of the process. Fingerprints are commonly used in relation to:

  • Warrants and extradition: police officers and jailors use such identification to confirm a suspect's identity and to facilitate arrest.
  • Charging decisions: Positive and negative conclusions on fingerprint identification evidence determine the strength of the case and the appropriate charges to file
  • Jury Trials: Latent fingerprint examiners, which are the prosecution's expert evidence also use this type of evidence to conclude whether the fingerprints of the accused match those found at the crime scene.
  • Appeals level: fingerprint identification evidence is used to bolster the prosecution's argument that the jury's verdict was appropriate and that any other alleged error at trial should be viewed as harmless error considering the strong weight of the fingerprint identification evidence.

Types of Fingerprints

There are two types of fingerprints:

  • Rolled or inked prints: obtained by individuals inking their fingers and rolling each fingertip from edge to edge on paper - these are also called known fingerprints because the identity of the person is known when they are taken and
  • Latent fingerprints: obtained by using fingerprint powder to make the latent print visible. Once the latent print is made visible, tape is used to lift the latent print from its original surface onto a lift card. These lift cards are examined by fingerprint identification experts who compare the friction ridge detail in the known print. Both types are utilized in the criminal justice system.

Methodology: ACE-V

Fingerprint examiners carry out a visual comparison of a crime scene mark (fingermark) and prints from a known individual (fingerprint). These sources are both impressions that are used in comparison process realized by the fingerprint specialists. A mark left on a surface is generally being compared with a print taken in controlled conditions for example using ink or, in current practice, ‘Livescan’, an optical device used to capture impressions digitally.

The comparison process is to determine whether a mark and a print match so that the mark can be ‘individualised’. By the mark being ‘individualised’ fingerprint examiners mean that it can be attributed to the known individual to the highest level of specificity: it is unique to that one individual out of the whole human population.

Most examiners use the comparison methodology that is called “ACE-V”.

ACE-V is an acronym of words that refers to the sequence of working scientific method whereby:

1. An examiner analyses a mark. The purpose of the analysis is to assess the quantity, quality and specificity of the present fingermark. In this stage, expert tries to assess the evidentiary value of the fingermark (i.e., its intrinsic value for discriminating a unique source).

2. Having done so the examiner compares the mark to a known print. If the mark determined to posses sufficient value, and the known exemplar is also sufficient for comparison purposes the expert proceeds the comparison phase. The comparison is the side by side comparison of the images. Features present in one image should be found in the other one, in the same relative position, orientation and number of intervening ridges.

3. Having compared the images the examiner evaluates what he or she has seen and reaches a decision. After the side by side comparison is complete the expert must formulate an opinion about the sources of the images. The decision making process is the stage of evaluation, where one of three general categorical conclusions is possible: individualization (identification), exclusion and inconclusive opinion.

4. The results of the evaluation stage are then subject to verification by one (or more) additional examiner(s). Finally, a review of the conclusion by another examiner or examiners, using the ACE process, provides a cross-check to ensure that the decision is not based on a marginal subjective judgment of one individual but enjoys acceptance as the consensus conclusion of a number of examiners. This check is a quality assurance mechanism and is the final phase of the ACE-V[4].

Standards for Identification

Notes

  1. FEJA Website: www.feja.am
  2. See Fingerprint, http://en.wikipedia.org/wiki/Fingerprint
  3. See Interpol, Fingerprints, www.interpol.int/content/.../14/.../Factsheets_EN_feb2012_FS03.pdf
  4. See The Fingerprint Inquiry Report. Scotland. Published on Behalf of The Fingerprint Inquiry by APS Group Scotland. Vol. 1, 2011, Ch 36; Jamieson Allan, Moenssens Andre (eds. in chief) Wiley Encyclopedia of Forensic Science. Chichester: Wiley, 2009, Vol. 3, pp. 1286-1287.

See Evidence