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If you have done nothing wrong, you needn't worry when the police come knocking on your door. That is what most people think. But just imagine: you are on your summer holidays, you go from one party to the other. The days are stringing into an endless blur. At the end of the summer, the police suddenly turn up on your doorstep. A student was raped in the area. She saw the culprit and you apparently fit the description: dark-skinned, 1.80 in height, 80 kilos and a thin moustache.
Where were you on the night of 28 July, the policeman asks?
Well, let’s see; then you remember that you visited your brother and afterwards went for a drink with friends. A couple of days later, you are talking to your mother. She says that you made a mistake: you spent the night at her place and slept on the sofa. Oh dear, you panic, you gave the wrong alibi. And then after all that, the student picks you out of a line-up as the culprit. For the judge, it is an open-and-shut case: life imprisonment!
This is not fiction, it really happened, in the US in the nineteen-eighties. Robert Cotton was his name. He was released after ten years, when a DNA investigation proved that he couldn't possibly be the offender.
Cotton is not the only innocent person who ends up in trouble because of a weak alibi. In 68 per cent of all miscarriages of justice in the US, it's the alibi of those who are wrongly convicted that is at some stage not believed, says Ricardo Nieuwkamp, who recently completed his PhD on this subject. His research shows that a mere 2 per cent of those who are innocent are capable of coming up with a credible story.
How is that possible? Investigators set the bar too high, expect innocent people to come up with strong evidence. That could be proof by a witness, where the standard is: the more distant, the more credible. A statement from someone living in the same street lends more weight than one from a son or daughter. Other strong evidence is tangible evidence, preferably surveillance tapes. Or proof of knowledge: you know something that others couldn't possibly know. You were in a traffic jam that hadn't been broadcast.
Something that happens much more often, certainly where it concerns a rape that took place at night, is the fact that most men are in bed with their wives, says Nieuwkamp. “That is weak evidence, so you continue to be a suspect. Certainly if you make a mistake and change your alibi. Your credibility drops immediately. While the mistake is often made because you are stressed during the interrogation. Investigators generally don't have any idea of how overwhelming that can be.”
Moreover, many policemen have opinions about memory that are quite out of tune with modern research. “They often think that the brain works like a video recorder that you can rewind to the day of the crime. Unfortunately, the brain makes more mistakes than you think.”
Nieuwkamp, who now works for the Belgian Vias institute and is carrying out research into road traffic safety, knows that a mere 14 per cent of the investigators who participated in his study, followed a course on evaluating alibis. “There is clearly a need for more attention for this subject in the curriculum,” says Nieuwkamp. That is the reason why he, together with the Dutch Police Academy, is going to look into how his results can be incorporated in the training programme.
Myth busters is a series in which academics shoot down popular myths on complex topics