The FBI has admitted to overstating nearly all forensic matches from suspects’ hair samples during a span of nearly 30 years.

Almost every FBI laboratory examiner – 26 out of 28 – had exaggerated matches so that they favoured the prosecutors’ arguments, according to The Washington Post.

More than 95 per cent of all 268 trials involving hair that were reviewed have been found to be unreliable in proving guilt of the serious crimes such as murder and rape.

Thirty-two of the defendants, in the cases from 1972 to 1999, were sentenced to death and 14 of those have since been executed or died in prison.

Forensics: The Anatomy of Crime Show all 5 1 /5 Forensics: The Anatomy of Crime Forensics: The Anatomy of Crime Forensics: The Anatomy of Crime Details from 'Identification Anthropométrique': the nose Wellcome Images Forensics: The Anatomy of Crime Forensics: The Anatomy of Crime Details from 'Identification Anthropométrique': the ear Wellcome Images Forensics: The Anatomy of Crime Forensics: The Anatomy of Crime A schematic diagram of the ear Wellcome Images Forensics: The Anatomy of Crime Forensics: The Anatomy of Crime A prison mug-shot album (1883–89), contemporary with the work of Bertillon Wellcome Images Forensics: The Anatomy of Crime Forensics: The Anatomy of Crime Bertillon, in 1913, demonstrating the two-part 'mug shot' method of photographing suspects Wellcome Images

The FBI results do not mean there were not other pieces of evidence that had “proved” guilt of a crime, The Washington Post states, however prosecutors and defendants are being told whether there would be grounds for them to appeal.

Four convicts, three from Washington DC and one from Florida, have since been exonerated based on the findings.

The review is being spearheaded by the National Association of Criminal Defence Lawyers and the charity Innocence Project.

Around 2,500 cases in total have been earmarked for review by the FBI.