ID by fingerprints: not fact but opinion

By Anna Sandiford 29/05/2012

Many people in New Zealand still seem unaware of the substantial shake-up going on in forensic science globally. Alot of it has come from the USA National Academy of Science’s review on forensic science. Some has come from the UK Law Commission’s review of forensic science practices. One of the many areas of interest is fingerprints.

Fingerprints is one of those areas of expertise on which the courts have traditionally placed enormous weight in terms of confirming the identification of an individual. In reality though we know that fingerprint identification is not infallible – you only have to look at the Madrid bombing case, which was probably one of the world’s most spectacular examples of mis-identification using fingerprints. A fingerprint was lifted from plastic bags that contained detonator caps and a match was made by the FBI with an American lawyer called Brandon Mayfield, despite Spanish authorities advising the FBI that Mayfield was not a match. In a statement eventually released by the FBI they stated:

“The FBI identification was based on an image of substandard quality, which was particularly problematic because of the remarkable number of points of similarity between Mayfield’s prints and the print details in the images submitted to the FBI. The FBI’s Latent Fingerprint Unit will be reviewing its current practices and will give consideration to adopting new guidelines for all examiners receiving latent print images when the original evidence is not included.”

This is a good example of why it is always best practice to look at the original item and not use digital images or copies.

A more recent report came out of the Scottish Fingerprint Inquiry that followed from the case of HM Advocate v McKie. In that case, Shirley McKie was a police officer who attended the scene of a murder as part of the police investigation team. Of the 428 fingerprint marks lifted from the scene, one was identified as having been made by Ms McKie. During the trial of the accused, Ms McKie was a witness and she asked about the fingerprint attributed to her. She did not accept that the mark was made by her; the mark in question was found inside the house and she said she had not entered the house beyond the porch. The defendant was found guilty and after the trial Ms McKie was charged with perjury and was herself tried. Two well-known international fingerprint experts disputed the finding that the fingerprint attributed to Ms McKie was made by her. She was found unanimously not guilty by a jury.

One of the key findings of the Fingerprint Inquiry was that:

“Fingerprint evidence should be recognised as opinion evidence, not fact, and those involved in the criminal justice system need to assess it as such on its merits.”

The Inquiry went on to say that:

“Examiners should discontinue reporting conclusions on identification or exclusion with a claim to 100% certainty or on any other basis suggesting that fingerprint evidence is infallible.

Examiners should receive training which emphasises that their findings are based on personal opinion; and that this opinion is influenced by the quality of the materials that are examined, their ability to observe detail in mark and print reliably, the subjective interpretation of observed characteristics, the cogency of explanations for any differences and the subjective view of ‘sufficiency’.

These findings are further corroborated by the February 2012 report of the Expert Working Group on Human Factors in Latent Print Analysis (USA National Institute of Standards & Techology/National Institute of Justice) in which Recommendation 3.7 is as follows:

“Because empirical evidence and statistical reasoning do not support a source attribution to the exclusion of all other individuals in the world, latent print examiners should not report or testify, directly or by implication, to a source attribution to the exclusion of all others in the world.”

The summary points I have extracted above are, of course, nowhere near the total amount of information available in these reports; the full reports can be read at leisure. However, the issue that I want to establish here is that yes, mis-identifications may be rare but the fact that it can happen is one of the factors that led to the Scottish Fingerprint Inquiry stating that fingerprint analyses should not be considered evidence of fact.

Fingerprint examination and interpretation is opinion evidence, not fact. Accordingly, the results should be worded accordingly and, in the adversarial system, can be challenged as opinion evidence, just like many other areas of forensic science.