By Andy Coghlan
September 22, 2011
Troy Davis, convicted in 1991 of killing an off-duty police officer, was last night executed in Jackson, Georgia, despite an international campaign to throw out the conviction.
The execution, backed by the US Supreme Court, brings to an end a sustained campaign to clear Davis on the grounds that witnesses misidentified him as the murderer of Mark MacPhail.
Seven of the nine original witnesses in the case have since recanted their statements in sworn affidavits, throwing the spotlight back onto the reliability of witness statements. Some of the jurors have also changed their minds about Davis’s guilt.
The issue of witness reliability will arise again on 2 November when the Supreme Court hears the case of Barion Perry versus the state of New Hampshire, in which a single witness identification was central to Perry’s conviction for robbing a car in 2008.
Last month, the supreme court of New Jersey became the first in the US to issue strict new rules on the admissibility of witness identification. As a result, judges in New Jersey must now warn juries on the potential shortcomings of each witness’s evidence.
In the Davis case, MacPhail died coming to the aid of a homeless man who was being pistol-whipped by two assailants, one of whom turned the pistol on MacPhail and fatally shot him.
Taken together, the recanted witness statements paint a picture of witnesses being bullied by police into identifying Davis as the murderer. “They made it clear that the only way they would leave me alone was if I told them what they wanted to hear,” said one witness, Jeffrey Sapp.
According to Amnesty International USA, many witnesses identified Davis from a photo array after his picture had been “plastered all over the media”, potentially priming the witnesses to pick him simply through prior assumptions linking his face with the crime.
As a prelude to the upcoming Perry case, the American Psychological Association (APA) has given the Supreme Court a summary of the scientific consensus on the pitfalls of witness identification.
The brief states that in controlled experiments and studies of real cases, misidentification occurs around a third of the time.
It cites research showing that juries tend to “overbelieve” witnesses, giving their testimony disproportionate weight over other evidence: witnesses are often mistaken about their recollection of events, but juries believe them because of their passionate conviction that they are correct.
The brief points out that of the first 200 cases in which convicted individuals were later exonerated by new DNA evidence, almost 80 per cent included at least one eyewitness who mistakenly identified the innocent defendant.
The APA also cites evidence showing that police can secure positive identifications through pre-suggestion. The tactic most open to abuse is a so-called “show up”, when a police officer shows a picture of the suspect to a witness and asks: “Was this the perpetrator?” Research shows that this produces twice as many false identifications as line-ups, in which witnesses are shown a group of people who include the suspect and asked if they recognise the perpetrator.
The APA says that there are many other more innocent factors that can affect the reliability of a memory. These include the time that has elapsed between the event and the identification, the stress the witness suffered during the crime, the length of time for which the witness saw the perpetrator, the distance between the perpetrator and the witness, the brandishing of a weapon at the scene and racial differences between the witness and perpetrator.
Time and distance
In one study, witnesses viewed a video of a crime and then tried to pick out the perpetrator from an array of photos. The accuracy rate was 85 to 95 per cent when volunteers had spent 45 seconds watching the video, but fell to 29 to 35 per cent after a viewing of just 12 seconds.
The association also reports that the ability to identify a face falls away at around 8 metres, disappearing almost completely at 45 metres.
Given these shortcomings, the outcry over the Davis case may now add to pressure on the US Supreme Court to follow New Jersey’s lead of treating witness statements with greater caution when the Perry case comes up on 2 November.