"I'm sort of a neuroscientist by training and a crime fighter almost by happenstance," he says.
Dr. Farwell calls his invention brain fingerprinting. It's based on the widely accepted theory that when people are presented with familiar information, like words or images, their brains unconsciously emit special electrical signals called brain waves.
Here's how it works: Farwell flashes the subject photos or phrases describing important details of the crime scene, which he calls probes. If a person recognizes those probes, his brain will generate a particular kind of brain wave. If a person, the brain's response is noticeably different.
And because brain waves are involuntary, the theory goes, it's impossible to conceal the truth: "The perpetrator, having committed the crime, has those details stored in his brain. The innocent suspect doesn't," Farwell said.
Many scientists have recorded these kinds of brain waves in the lab, but Dr. Farwell, a Ph.D. with a black belt in kung-fu, is the first to try to apply this science to real-world criminal cases.
Farwell's work was taken seriously enough by the CIA that in the early 90s they funded some of his research. The FBI also let him run a successful experiment at its Quantico training center.
Over the past year, 48 Hours has followed Farwell as he worked almost exclusively on the case of Brad Harris and his brother, Danny. They were convicted in 1987 of murdering their neighbor, 16-year-old Kris Nelson in Council Bluffs, Iowa. Kris' body was discovered by the bank of the Missouri River. She'd been raped, stabbed and beaten to death.
Despite his protests of innocence, a jury convicted Danny, then 21, of felony murder and sentenced him to life in prison; his younger brother Brad pleaded guilty to second-degree murder and served 4 ½ years.
Why would Brad agree to a plea if he had no role in the murder?"
"Because they'd already convicted my brother on first-degree murder on something he didn't do," Brad tells correspondent Troy Roberts.
Dennis Whelan, a private investigator in Council Bluffs, and his son Mick, an attorney, believe the brothers are innocent and were framed.
Old friends of the Harris family, they've spent more than 10 years working at their own expense to clear the brothers.
Despite their years of effort, Dan Harris has remained at the Iowa State Penitentiary, unable to get a new trial. Then last year, after exhausting other alternatives, the defense turned to Dr. Larry Farwell and his controversial brain fingerprinting technique.
To conduct his test, Farwell first examines the case file, and visits the crime scene, searching for potential memory probes.
Farwell decides the murderers would have to remember the place where Kris was initially attacked, the place where her body was found and the process of dragging her body through the underbrush, across what was then sand to the riverbank.
These are details Farwell used to test the Harris brothers. Farwell uses pictures, or in Brad's case, phrases, as stimuli. The phrases describe how Kris's body was dragged through bushes, dragged across sand, and left half submerged in the water.
Farwell's conclusion: Brad does not recognize the probes.
After months of waiting, Farwell gets court permission to administer a brain fingerprinting test to Danny, who is sure that Farwell's technology will help overturn his life sentence.
But plenty of other people think Dr. Farwell's science, is a little far out.
"There's a lot of work that needs to be done before it can be used in a practical situation, and that work has never been done," says Professor Emmanuel Donchin, Farwell's mentor years ago at the University of Illinois.
He and Northwestern University's Peter Rosenfeld, are both leaders in the field of brain wave research. They agree with the theories behind Farwell's work, but say his test is too unreliable.
"Do you remember everything that you've done in the last several weeks or years? I certainly know I don't," says Rosenfeld. Farwell says brain fingerprinting, like any testimony, needs to be taken in the context of knowing memory is fallible - and a judge and jury have to take that into consideration.
Iowa prosecutor Rick Crowl is as skeptical of brain fingerprinting as he is confident in the guilt of Danny Harris.
"There was a fair amount of physical evidence tying him to the crime scene," Crowl says of Harris.
To settle the matter, Crowl took the highly unusual step of getting court permission to run DNA tests on semen found on Kris Nelson. "We obviously want to make sure we have the right people in prison," he says.
Farwell measures Danny's brain waves to see if he recognizes details of the Nelson murder. The results are immediately clear to Farwell: Danny Harris does not recognize the crime scene.
"This is very solid evidence that what you said is accurate," Farwell tells Danny. "That you weren't there because you don't know these things."
But weeks later, the state's DNA test results come in. The test concludes that semen found on Kris Nelson matched Danny Harris'. His defense team, lead by Denny and Mick Whelan, claim the sample was contaminated.
Why would someone want to tamper with the DNA test? "Because they don't want to admit they were wrong," Danny says.
Farwell says, "What I can tell you as a scientist is that the record stored in Danny Harris' brain doesn't match the crime scene."
Why are the results of the two tests contradictory? "They're not contradictory, because they're measuring different things," Farwell says.
Even Farwell's harshest critics concede that brain fingerprinting could one day prove useful. But many think that Farwell, like many inventors with a passion, may be pushing his technology too far, too fast.