The aftermath of the shooting of Jean Charles de Menezes at Stockwell Tube station has shown that eyewitness testimony may not always be as reliable as it seems.
On the day Mr Menezes was killed, a picture was quickly painted by eyewitnesses of a suspect who had vaulted over a ticket barrier, ran away from police, and had worn a bulky jacket that could have concealed a device.
Scotland Yard did nothing to dispel that impression, saying that the shooting had been "directly linked" to anti-terrorism operations, that Mr Menezes had been challenged but had not obeyed, and that the victim's "clothing and behaviour" had added to suspicions.
Over the last month, the image of Mr Menezes' conduct has been slowly dispelled, before being completely shattered by Independent Police Complaints Commission documents leaked to ITV News.
According to the documents, Mr Menezes was wearing a light denim shirt or jacket, walked through the barriers having picked up a free newspaper, and only ran when he saw his train arriving.
It has left many scratching their heads as to how the witnesses could have got it so wrong.
The reliability of eyewitness accounts of crime has proved a rich seam for psychologists and criminologists to mine over the years.