An important part of the scientific process involves recognising human bias and preventing it from affecting results. For that reason, scientists use double-blind studies. When evaluating a drug for clinical trials, neither the doctors nor the patient knows who has been given the experimental drug and who the placebo. It is only after the experiment has been concluded that the scientists are unblinded. That way their wishful thinking can’t influence their findings.

Not so with the legal profession, which accumulates biases every step of the way. Most police, when they show a line-up to a witness, know which face belongs to the suspect. Studies have shown that that simple knowledge can lead an officer to unconsciously influence the witness who, in turn, can pick the favoured suspect, who might not be the perpetrator.