The Controversial Rise of Criminal Brain Science in US Courts

Kent Kiehl loves to talk about the criminal defendant who first put his controversial brain research on the map, the serial killer Brian Dugan.

“He was just utterly and completely psychopathic. A perfect – I mean, I hate to say this word – specimen.”

In 2009, Dugan’s lawyers asked Kiehl to testify about Dugan’s inclination for killing.

At the time, a jury in Chicago was deciding whether to sentence Dugan to death for the rape and murder of a 10-year-old girl. Dugan had already confessed to the murder in 1985, while he was serving a life sentence in state prison for the rape and murder of two other women. DNA evidence later established that Dugan had been at the crime scene.

In the words of one of Dugan’s attorneys, the case was “a slam dunk for the prosecution”. Out of desperation, they summoned Kiehl, a researcher at the University of New Mexico who has made it his specialty to study the brains of the incarcerated, as their star witness.

Dugan was certain to be found guilty. But, were a brain scan to identify him as psychopathic, his attorneys could argue in court that Dugan should not be sentenced to death because he was not emotionally capable of sensing right from wrong.

Kiehl thought he might have the answer Dugan’s defense attorneys wanted. He tested Dugan’s brain the same way he had tested more than 1,000 prisoners before. He interviewed him for hours, then applied his answers to a psychopathy checklist that screened for 20 traits and behaviors, like “grandiose sense of self-worth” and “pathological lying”, and assigned each trait a score. Dugan’s checklist score met the threshold for a psychopath, so Kiehl scanned his brain using what was at the time a new technique, called functional magnetic resonance imaging (fMRI), to search for any brain abnormality that might explain Dugan’s psychopathy.

During fMRI scans, researchers map which brain regions are activated in response to certain images. Kiehl scanned Dugan as he was shown pictures designed to provoke emotional responses, like a man yelling at a child or a surgical procedure.

“His score is in the highest range of any of the inmates I’ve ever met,” Kiehl told the jury, referring to Dugan’s score on the psychopathy checklist. “He’s had these symptoms and problems from a very early age.”

In an autobiographical account of his research, published five years later, Kiehl wrote that the scans showed Dugan’s brain was “atrophied”.

Dugan’s trial, 17 years ago, was one of the first US court cases to admit brain research as evidence. The case made national news. But Kiehl’s evidence didn’t convince jurors to be lenient. They sentenced Dugan to death. His sentence was later commuted to life in prison, only after the state of Illinois imposed a moratorium on the death penalty.

But what happened in the aftermath was seismic. In the years that followed Kiehl’s testimony, the science of biological criminality, though shaky, was invoked in thousands of cases. Defense attorneys, in particular, used biological evidence like brain scans to argue that their clients should receive lighter sentences.

From 2005 to 2015, the use of brain evidence in criminal defenses appeared in more than 2,800 judicial opinions, according to a 2019 study. The researchers estimated that neurological arguments for reduced criminal responsibility appeared in roughly 10-12% of US murder trials, about 25% of death-penalty trials. Overall, 40% of serious felony cases referred to brain-based evidence.

Even those figures don’t fully capture the prevalence of neuroscience-based evidence in criminal cases in the US. The study acknowledges that the 2,800 figure “likely underrepresents” such evidence, since it only captures published judicial opinions that reference brain-based arguments.

The biological argument in many of these cases is roughly similar. Echoing Kiehl’s research, attorneys would argue that some people are just programmed for criminal behavior, through no fault of their own.

Few scientists have pursued that argument more aggressively than Kiehl, who, after Dugan’s trial, became the public face of criminal brain science. He has spent the last two decades sending his mobile MRI machine to prisons and jails across the US, in an attempt to identify people with a “criminal brain”.

Critics argue these claims outrun the science, reviving an old and long-debunked idea: that criminality can be read in the body – a modern echo of eugenic thinking that once influenced US courts and public policy.

In the US, where people of color are disproportionately arrested, tried and convicted at higher rates than white people, evidence that relies solely on biological factors is also ethically dubious.

But beyond the disputed nature of the science, using biological evidence in courts can also be a double-edged sword. While defense attorneys have used it to argue for lighter sentences, it is sometimes used to make the case for more severe punishment by suggesting that some people will for ever be prone to violence.

Despite these misgivings, criminal brain science, a long discredited relic of scientific history, has returned.

The stakes are profound. A body of science that many researchers describe as unreliable has now become routine in capital cases. In US courts, this illusion of scientific certainty has led to some defendants being sentenced to death.

Kiehl likes to talk about the many occasions on which he has sat across from a prisoner and identified them as a psychopath. “They’re so utterly and totally different than the rest of us,” he says, gleefully. “It’s totally shocking … I just love it.”

He boasts about his bravery around those with criminal pasts. Most other psychopathy researchers “are never going to go into a maximum-security prison. They never could, they just wouldn’t,” he said. “It’s because it’s scary.”

Kiehl, 56, speaks in a high nasal pitch and delivers his thoughts in a rapid-fire narrative style.

During three lengthy phone interviews between November 2023 and February 2024, Kiehl described himself as an iconoclastic researcher who hoped that scientists can one day find a cure for criminal violence. He even invited me to his lab to scan my brain and experience his methodology for myself. (A week before I was due to travel to New Mexico, he rescinded the invitation and has since refused my requests for further interviews and the opportunity to comment on this story.)

Kiehl grew up in Tacoma, Washington – about a mile from the home of Ted Bundy, the notorious American serial killer.

Kiehl’s father, a reporter and news editor, covered Bundy’s criminal trial for the local paper. His childhood friends refused to go anywhere near the areas where Bundy had murdered his victims. But being so close to the horror sparked his interest in studying the human capacity for destructive behavior. “Where I grew up, there was this fear. And I just remember that there was just no one who studied them,” Kiehl said of serial killers.

Kiehl’s mother was 16 years old when she had him, he said, and he spent the first two years of his life in an orphanage. A Catholic couple in Tacoma adopted him. He learned of his adoption at around age 12, on a family vacation in Phoenix, when one of his adoptive sisters blurted out the truth during a fight.

The revelation violated his sense of trust. After the fight, Kiehl briefly ran away from his family. “It definitely was a good excuse for some juvenile delinquency.”

But he was academic, and went on to study psychology as an undergraduate at the University of California, Davis, where he decided, by the end of his degree, “the number one thing I’d like to study is psychopaths”.

In the 1990s, if you wanted to study criminals, there was only one place to go, Kiehl said – the laboratory of Robert Hare at the University of British Columbia in Vancouver, Canada. He had pioneered psychological research on prison populations. So, Kiehl courted him.

It took over a year for Hare to accept Kiehl into his lab. To try to win him over, Kiehl said he drove through a snowstorm to Hare’s home and brought him bottles of wine. “He thought I was nuts,” he said. “I just said: ‘I might not be your smartest student, but I will be the hardest-working student you’ve ever had.’”

Hare told me by email that he hesitated in accepting Kiehl because “his first few years at Davis were not impressive”.

Kiehl said he would never forget the day Hare relented. “He just called me and told me that he was going to accept me and that he expected big things out of me.”

Kiehl has remained in academia ever since. In 2007, he accepted a neuropsychology position at the University of New Mexico. His university webpage proclaims that his laboratory, which operates under the Mind Research Network in Albuquerque, has created “the world’s largest database of brain data” from incarcerated people.

Today, Kiehl is one of the few remaining contemporary scientists in America who concentrate their research on the incarcerated. (Criminal neuroscience is an insular field, populated by a small group of researchers whose papers often trace back to Kiehl.) His theories have been used by defense lawyers trying to convince juries that their clients had brains that predisposed them of violence.

One such defense, the 2013 case of Amos Joseph Wells III, shows how this approach can have grave consequences for defendants.

‘He didn’t ask for the brain he got’: the trial of Amos Wells

On 1 July 2013, at aabout 7.30pm, Amos Joseph Wells III walked into a police department outside Fort Worth, Texas, and told officers he wanted to die. “Put me in jail. Kill me,” he said.

A police sergeant noticed that Wells was sweating, with a “dazed, kind of spacey look on him”. “Something heavy was on his conscience,” another police officer noted.

Less than two hours before, Wells had shot his pregnant girlfriend, Chanice Reed; her mother, Annette Reed; and Chanice’s 10-year-old brother, Eddie McCuin.

After the shooting, Wells called the mother of his child, Valricia Brooks, and asked to speak to his young daughter. He told her he loved her and to be a good girl. He told Brooks he was planning on killing himself. “I don’t know why I did it. I don’t know why I killed them,” he told Brooks, crying.

Wells later testified that a hallucination of a man in white pointed him toward the police station. When he confessed to the shooting, a detective informed Wells that Chanice, Annette and Eddie had all died. Video footage captured the detective embracing Wells in the interrogation room.

The state of Texas charged Wells with capital murder. He pleaded not guilty. Two state-appointed lawyers represented him at trial, where they introduced a bold defense.

“Amos didn’t ask for his genetics, he didn’t ask for the brain he got, and he darn sure didn’t ask for the parents he got handed.”

This was the closing statement Wells’s lead attorney presented to Texas jurors in 2016, while they were deciding whether to condemn Wells to death. He argued that his genetic makeup should give the jury “cause to pause” before imposing the ultimate penalty.

They had contacted Kiehl and his colleagues to scan Wells’s brain and conduct genetic testing in an attempt to bolster their argument that Wells was biologically prone to criminal violence.

It was a risky strategy.

Wells’s trial judge didn’t allow the jury to see video footage of his expressions of remorse during his police confession – evidence that his new attorneys, who have fought to get him off death row, say could have helped his case, along with a humanizing history of Wells’s troubled life and struggles with mental illness.

Instead, Wells’s own lead counsel explicitly told the jury that Wells had “no control” over his nature. The judge allowed this disputed science to stand as evidence that Wells would for ever present a future danger to society.

Court documents show that, by using the brain and genetic evidence, Wells’s trial attorneys had hoped to secure a sentence of life in prison. Instead, just as in Dugan’s case, the jury condemned Wells to death.

A decade on, Wells is now represented by attorneys at the international law firm Cooley LLP, who have urged the supreme court to intervene in the case. They argued that Wells’s trial was tainted by pseudoscience and racism, in violation of his constitutional right to effective assistance of counsel. The National Association for the Advancement of Colored People, the civil rights group, filed a brief in support of Wells, as did 29 scientists and lawyers, and representatives from two US law schools.

They believe the biological evidence Wells’s defense attorneys presented at trial, rather than help spare Wells’ life, made a powerful argument for his execution.

But what is it about the evidence presented in this case by Kiehl and his colleagues that these scientists and attorneys find so troubling? And what does it mean for the thousands of other cases that rely on similar evidence?

Picking up where phrenology left off

To understand what went wrong in Wells’s case, it’s helpful to first understand that Kiehl’s hopefulness about discovering the biological roots of criminality, and their potential to remake the criminal legal system, are part of an old and tragic tale.

For more than two centuries, scientists have entered the public arena claiming to have decoded criminality in the human body. Legal practitioners have embraced the science, infatuated by the idea that, under criminal law, human beings may no longer be judged by what they do, but by who they are.

In the early 19th century, the science of biological criminality was called phrenology.

Austrian anatomist Franz Joseph Gall had developed theories of criminal behavior by examining the heads of people convicted of crimes. He ascribed arbitrary terms such as “combativeness” and “destructiveness” to bumps and hollows in their skulls. Through the right types of brain exercise, phrenologists proposed, people could change their brains and characters.

In the US, judges used phrenology to assess the mental states of people on trial for murder, lawyers introduced it at criminal trials to argue for lighter sentencing and police departments used it to determine who might commit future crimes.

Yet by the late 1800s, phrenology had been discredited and was banned from many parts of the US.

A young Italian doctor, Cesare Lombroso, picked up where phrenology left off. While working at an Italian asylum through the late 1800s, he opened the skulls of people incarcerated there and claimed to find evidence of abnormal brains in those who had been convicted of crimes. He wrote the criminal brain resembled that of “the rodent or lemur, or the brain of a human fetus of three or four months”.

By the mid-20th century, biological theories of criminal behavior had fallen out of favor again, carrying the memory of Nazi Germany, where ideas of innate criminality were used as a tool of social co