Police come to your door, grab you, take you to the cop shop and stick electrodes on your head. You are not asked anything at all. Instead, you lay there silently, watching pictures of a crime flash before your eyes.

Ten minutes later the police tell you that you are found guilty of the murder of a young woman called Sally. No further questions are asked - your brain has told them everything!

Brain fingerprinting is a technique developed by Dr Lawrence Farwell, neuroscientist and chairman at Brain Fingerprinting Laboratories Inc. Suspects are presented with a jumble of words, pictures and images - some of them relevant to the crime, others unrelated. When the relevant stimuli are presented, the suspect lets off a involuntary, specific, and measurable brain response known as a P300.

Dr Farwell told BBC news that “brain fingerprinting doesn’t have anything to do with the emotions, or whether a person is sweating or not; it simply detects scientifically if that information is stored in the brain.”

Farwell Brain Fingerprinting has proven 100% accurate in over 170 tests on FBI agents, US Marines and real-life suspects. If brain fingerprinting proves as foolproof as early research suggests, it could create a legal revolution.

Its effect has already been felt in the United States criminal justice system. On April 25, 2000, Dr. Farwell used Brain Fingerprinting to exonerate an Iowa man who spent 23 years in prison for a crime that he did not commit. Brain fingerprinting results showed that the man's brain did not contain details of the crime that would be known to the perpetrator. But he did have memories stored in his brain that matched several alibi witnesses, who testified that he was elsewhere at the time of the crime.