Criminals convicted primarily on the basis of fingerprint evidence could soon have grounds for appeal based on the comments of a leading forensic scientist.Fingerprint evidence has been employed to establish criminal involvement since forensic science was first used by the UK’s Scotland Yard back in 1901, but now Mike Silverman, who introduced the first automated fingerprint detection system to the Metropolitan Police, believes that this method of establishing guilt is not as reliable as previously thought.

Human error, partial prints and false positives all add to the inaccuracy of the evidence, says Silverman, but there is also concern that it has never been possible to prove that fingerprints are one hundred per cent unique; consequently, it must be acknowledged that there is the potential for "fingerprint twins" to exist. True, evidence to date suggests that it would be more likely for a person to get struck by lightning or win the lottery than to meet another "fingerprint twin" , even assuming that such twins exist, but a question mark must now hang over the reliability of such evidence.

In fact, unique prints have never been considered to be a certainty; the concept was first introduced after research by Scottish surgeon Dr Henry Faulds, who collaborated with Charles Darwin and his cousin Francis Galton, and Galton subsequently wrote a book claiming that the likelihood of two people having identical prints was around 1 in 64 million.Despite having originally rejected Faulds’ proposals for the use of fingerprints in forensic science, the odds put forward by Galton were sufficient to tempt Scotland Yard of their promise in the field of criminal identification, where they have been used ever since.

Mike Silverman, the U.K. Home Office’s first Forensic Science Regulator, said: “Essentially you can’t prove that no two fingerprints are the same. It’s improbable, but so is winning the lottery, and people do that every week.

"No two fingerprints are ever exactly alike in every detail, even two impressions recorded immediately after each other from the same finger.

“It requires an expert examiner to determine whether a print taken from crime scene and one taken from a subject are likely to have originated from the same finger.”

Even if identical fingerprints do not exist, it has been shown that families can share similar elements of the same pattern. The passage of time can also affect the accuracy of fingerprinting; old samples from the same person could differ from their current prints due to the loss of skin elasticity. Some rare skin conditions can erase the patterns on finger tips and change the nature of the print.

Interpretation of fingerprint evidence can also be very subjective, and a study conducted at Southampton University discovered that, in two thirds of cases, experts who were unwittingly presented with the same sets of prints more than once came to a different conclusion on each occasion.

“What both cases clearly demonstrate is that, despite the way fingerprint evidence is portrayed in the media, all comparisons ultimately involve some human element and, as a result, they are vulnerable to human error,” said Mr Silverman, an experienced forensic scientist and author of a recently published casebook of memoirs entitled ‘Written in Blood’.

Silverman, who now works as a private forensic consultant, has called on his own extensive experience to highlight doubts surrounding the quality of fingerprint samples, particularly as the evidence carries such weight in the courtroom. Fingerprint examiners must usually testify to the fact that fingerprint samples are either a 100 per cent certain match or a 100 per cent exclusion, with no margin for human error, unlike other forensic fields, such as DNA analysis, which merely suggest a statistical probability of a match.

“The fingerprint often isn’t perfect, particularly at a crime scene, he explained. " It might be dirty or smudged. There are all sorts of things that reduce the accuracy. think it is important that juries are aware of this. Too often they see programmes like CSI and that raises their expectations. What you see on CSI or Silent Witness simply doesn’t exist.”

Silverman’s concerns are not without foundation: there are several cases in history where wrongful convictions have been made based on dubious fingerprint samples.

In 1997, Scottish police office Shirley McKie was wrongly placed at a murder scene when a print that supposedly matched her own was found near the murder victim, and in 2004, Brandon Mayfield, was wrongly linked to the Madrid train bombings by FBI fingerprint experts in the United States.

Silverman believes that the situation has been further compounded in the U.K. by the fact that police forensic services have now been outsourced to the private sector, and that this could result in further miscarriages of justice in the future.

“Police forces have to slash their budgets and the easy thing not to spend money on is forensic services,” he said.“You have to ask yourself what price you put on justice.”

Fingerprint scanners are now even available as apps on smartphones, but it appears that fingerprints could and should soon be phased out as a viable method of security identification, particularly as science is rapidly providing viable alternatives. Scans of the iris and retina in the eye have been around for some time now, but new bio-identification markers are being constantly explored and have now expanded to encompass individual scent, heart-rate, vein-scanning and even butt shape!

It is hoped that these would provide a more secure means of identification: fingerprint scanners cannot detect whether a fake finger is being used, but the latest techniques would be much more difficult to circumvent.As security becomes more of an issue in our technological age, it is estimated that by the end of next year up to 619 million people could be using some form of biometric security device on their mobile devices.

Bioemetrics are of less help to forensic science, however; fingerprints may be unreliable, but for now they remain one of the few residual traces left at the scene of a crime. It seems unlikely that a criminal would leave a usable butt-print. For now, fingers will continue to do the talking.

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