Imagine a crime scene. There is a suspect, but he is innocent until proven guilty. This is where brain fingerprinting comes into play. It can be used to determine whether or not a suspect's brain recognises specific details. If it does, then the police will know their suspect has more information stored in his brain. Brain fingerprinting allows this by measuring a person's brainprint when he or she is shown a particular body of writing or an image.

The neurons in a brain fire electrically in synchronised patterns. Once the brain recognises something familiar, it will provide an instantaneous spark of recognition, something called the P300.
—"Fingerprint your brain," New Straits Times, June 11, 2006

A controversial technique for identifying a criminal mind using involuntary brainwaves that could reveal guilt or innocence is about to take centre stage in a last-chance court appeal against a death-row conviction in the US.

The technique, called "brain fingerprinting", has already been tested by the FBI and has now become part of the key evidence to overturn the murder conviction of Jimmy Ray Slaughter who is facing execution in Oklahoma.

Brain fingerprinting, developed by Dr Larry Farwell, chief scientist and founder of Brain Fingerprinting Laboratories, is a method of reading the brain's involuntary electrical activity in response to a subject being shown certain images relating to a crime.

Unlike the polygraph or lie detector to which it is often compared, the accuracy of this technology lies in its ability to pick up the electrical signal, known as a p300 wave, before the suspect has time to affect the output.

"It is highly scientific, brain fingerprinting doesn't have anything to do with the emotions, whether a person is sweating or not; it simply detects scientifically if that information is stored in the brain," says Dr Farwell.
—Becky McCall, "Brain fingerprints under scrutiny," BBC News, February 17, 2004

The Pottawattamie County Courthouse will become a legal testing lab this week as an Omaha man tries to overturn a 22-year-old murder conviction with a defense that includes new brain-wave technology that's never been used in court.

It's the first time anyone has tried to enter into evidence the results of a computer-generated test created by an Iowa psychiatrist, Lawrence Farwell, who calls the technology "brain fingerprinting." ...

After results of Harrington's test spread through the correctional system, other inmates wanted to be tested. The department now is trying to create a policy on how to allow more brain-fingerprint testing.
—Chris Clayton, "'Brain-Fingerprinting' Defense Gets Iowa Test," Omaha World-Herald, November 14, 2000