Researchers at the University of London used a suction device to create bruises on 11 subjects. They then took sequential photos of the bruises over nine days. They showed the photos to 15 forensic experts and asked them to order the photos chronologically. Forensic experts regularly testify about the age of bruises down to the hour, providing chronologies that allow prosecutors to give a suspect a window to have committed a crime. Or, alternately, to attempt to put a the crime at a time for which the defendant has an alibi.
But these particular 15 experts didn't fare so well. The results:
Lead author, Margaret Pilling, an Honours Medical Student at Barts and the London School of Medicine and Dentistry, said: "The greatest accuracy, from forensic experts, occurred in very fresh bruises (between 0 and 12 hours) however there were still a number of significant misjudgements in this age range.
"The median difference between the estimated age and the real age was 26 hours—a considerable disparity. We conclude that forensic experts' estimates of bruise age from photographs are, at best, unreliable."