10 December 2009


Section 76 of the Police and Criminal Evidence Act 1984 allows the Court, in a trial, to decide whether or not a confession is admissible as evidence.

When considering the admissibility of evidence, one has to constantly weight up its probative value (does it tell the court anything) against its prejudicial value.

This is what I thought of when reading the latest note from Mindhacks, "The persuasive power of false confessions".

The article discusses how people begin to disbelieve other evidence that may contradict a (false) confession, since a confession is given a greater weight.

"Imagine if an accused but innocent person falsely confesses and the other evidence doesn't suggest that they have committed the crime. In this situation, it turns out that both lay people and experts tend to change their evaluation of the other evidence and perceive it as being stronger evidence against the accused."

The Mindhacks note (like this post) is derivative and links to, "The Psychology and Power of False Confessions."

This article gives examples of the effect of other evidence being tainted by a confession. One of which refers to fingerprint evidence,

"In 2006, University College London psychologist Itiel Dror took a group of six fingerprint experts and showed them samples that they themselves had, years before, determined either to be matches or non-matches (though they weren’t told they had already seen these fingerprints). The experts were now given some context: either that the fingerprints came from a suspect who confessed or that they came from a suspect who was known to be in police custody at the time the crime was committed. In 17 percent of the non-control tests, experimenters changed assessments that they had previously made correctly. Four of the six experts who participated changed at least one judgment based on the new context. “And that’s fingerprint judgments,” Kassin said. “That’s not considered malleable. And yet there was some degree of malleability and one of the ways to influence it was to provide information about the confession.”"

Mmm, so there we have it. A method of manipulating evidence which will be known to every experienced detective wittingly or otherwise. As soon as the fingerprint examiner supports the detectives hunch, he can't go back on it.

Update 15th Jan 2010 - Mindhacks has dug up another article on false confessions, "...a suspect’s confession sets in motion a virtually irrefutable presumption of guilt among criminal justice officials, the media, the public and lay jurors. A suspect who confesses—whether truthfully or falsely—will be treated more harshly at every stage of the criminal justice process." The Mindhack article is based on, "The Problem of False Confessions in the Post DNA World" [pdf] and illustrates the importance of s76 of PACE.

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