On July 1, 2013, Amos Joseph Wells III went to his pregnant girlfriend's home in Fort Worth, Texas, and shot her multiple times in the head and stomach. He then killed her mother and her 10-year-old brother. Wells surrendered voluntarily within hours, and in a tearful jailhouse interview told reporters, "There's no explanation that I could give anyone, or anybody could give anyone, to try to make it seem right, or make it seem rational, to make everybody understand."
Heinous crimes tend to defy comprehension, but some researchers believe neuroscience and genetics could help explain why certain people commit such atrocities. Meanwhile, lawyers are introducing so-called neurobiological evidence into court more than ever.
Take Wells, for instance. His lawyers called on Pietro Pietrini—director of the IMT School for Advanced Studies in Lucca, Italy, and an expert on the neurobiological correlates of antisocial behavior—to testify at their client's trial last year. “Wells had several abnormalities in the frontal regions of his brain, plus a very bad genetic profile," Pietrini says. Scans of the defendant's brain showed abnormally low neuronal activity in his frontal lobe, a condition associated with increased risk of reactive, aggressive, and violent behavior. In Pietrini's estimation, that "bad genetic profile" consisted of low MAOA gene activity—a trait long associated with aggression in people raised in abusive environments—and five other notable genetic variations. To differing degrees, they're linked with a susceptibility to violent behavior, impulsivity, risk-taking, and impaired decision-making.
"What we tried to sustain was that he had some evidence of a neurobiological impairment that would affect his brain function, decision making, and impulse control," Pietrini says. "And this, we hoped, would spare him from the death penalty."
It did not. On November 3, 2016, a Tarrant County jury found Wells guilty of capital murder. Two weeks later, the same jury deliberated Wells' fate for just four hours before sentencing him to die. The decision, as mandated by Texas law, was unanimous.
In front of a different judge or another jury, Wells might have avoided the death penalty. In 2010, lawyers used a brain-mapping technology called quantitative electroencephalography to try to convince a Dade City, Florida, jury that defendant Grady Nelson was predisposed to impulsiveness and violence when he stabbed his wife 61 times before raping and stabbing her 11-year-old daughter. The evidence's sway over at least two jurors locked the jury in a 6-6 split over whether Nelson should be executed, resulting in a recommendation of life without parole.
Nelson's was one of nearly 1,600 court cases examined in a recent analysis of neurobiological evidence in the US criminal justice system. The study, by Duke University bioethicist Nita Farahany, found that the number of judicial opinions mentioning neuroscience or behavioral genetics more than doubled between 2005 and 2012, and that roughly 25 percent of death penalty trials employ neurobiological data in pursuit of a lighter sentence.
Farahany's findings also suggest defense attorneys are applying neuroscientific findings to more than capital murder cases; lawyers are increasingly introducing neuroscientific evidence in cases ranging from burglary and robbery to kidnapping and rape.
"Neuro cases without a doubt are increasing, and they're likely to continue increasing over time" says Farahany, who adds that people appear to be particularly enamored of brain-based explanations. "It’s a much simpler sell to jurors. They seem to believe that it’s much more individualized than population genetics. Also, they can see it, right? You can show somebody a brain scan and say: There. See that? That big thing, in this person’s brain? You don’t have that. I don’t have that. And it affects how this person behaves.”
And courts seem to be buying it. Farahany found that between 20 and 30 percent of defendants who invoke neuroscientific evidence get some kind of break on appeal—a higher success rate than one sees in criminal appeals, in general. (A 2010 analysis of nearly 70,000 US criminal appeals found that only about 12 percent of cases wound up being reversed, remanded, or modified.) At least in the instances Farahany investigated (a small sample, she notes, of criminal cases, 90 percent of which never go to trial), neurobiological evidence seemed to have a small but positive impact on defendants' outcomes.
The looming question—scientifically, legally, philosophically—is whether it should.
Many scientists and legal experts question whether neurobiological evidence belongs in court in the first place. "Most of the time, the science isn’t strong enough," says Stephen Morse, professor of law and psychiatry at the University of Pennsylvania.
Morse calls this the "clear cut" problem: Where the defendant's mental and behavioral state are obvious, you don’t need neurobiological evidence to support it. But in cases where the behavioral evidence is unclear, the brain data or genetic data aren't exact enough to serve as diagnostic markers. "So where we need the help most—where it’s a gray area case, and we’re simply not sure whether the behavioral impairment is sufficient—the scientific data can help us least," says Morse. "Maybe this will change over time, but that’s where we are now.”
You don't have to look hard to see his point. To date, no brain abnormality or genetic variation has been shown to have a deterministic effect on a person's behavior, and it's reasonable to assume that one never will. Medicine, after all, is not physics; your neurobiological state cannot predict that you will engage in violent, criminal, or otherwise antisocial activity, as any researcher will tell you.
But some scientific arguments appear to be more persuasive than others. Brain scans, for example, seem to hold greater sway over the legal system than behavioral genetic analyses. "Most of the evidence right now suggests that genetic evidence, alone, isn’t having much influence on judges and juries," says Columbia psychiatrist Paul Appelbaum, co-author of a recent review, published in Nature Human Behavior, that examines the use of such evidence in criminal court. Juries, he says, might not understand the technical intricacies of genetic evidence. Conversely, juries may simply believe genetic predispositions are irrelevant in determining someone's guilt or punishment.
Still another explanation could be what legal researchers call the double-edged sword phenomenon. "The genetic evidence might indicate a reduced degree of responsibility for my behavior, because I have a genetic variant that you don’t, but at the same time suggest that I'm more dangerous than you are. That if I really can't control my behavior, maybe I'm exactly the kind of person who should be locked up for a longer period of time," Appelbaum says. Whatever the reason for genetic evidence's weak impact, Appelbaum predicts its use in court—absent complementary neurological evidence—will decrease.
That's not necessarily a bad thing. There's considerable disagreement within the scientific community over the influence of so-called gene-environment interactions on human behavior, including ones believed to affect people like Amos Wells.
In their 2014 meta-analysis of the two most commonly studied genetic variants linked to aggression and antisocial behavior (both of which Wells possesses), Emory University psychologists Courtney Ficks and Irwin Waldman concluded that the variants appear to play a "modest" role in antisocial behavior. But they also identified numerous examples of studies bedeviled by methodological and interpretive flaws, susceptibility to error, loose standards for replication, and evidence of publication bias. "Notwithstanding the excitement that many researchers have felt at the prospect of [gene-environment] interactions in the development of complex traits, there is growing evidence that we must be wary of these findings," the researchers wrote.
So then. What should a jury consider in the case of someone like Amos Wells? In his expert report, Pietrini cited Ficks and Waldman's analysis—and more than 80 other papers—to emphasize the modest role of genetic variation in antisocial behavior. And in their cross examination, the prosecution went through several of Pietrini's citations line by line, calling for circumspection. They pointed to the Ficks paper, for instance. They also quoted excerpts that cast behavioral genetics findings in an uncertain light. Lines like this one, from a 2003 paper in Nature about the association of gene variants with anger-related traits: "Nevertheless, our findings warrant further replication to avoid any spurious associations for the example due to the ethnic stratification effects and sampling errors."
Pietrini chuckles when I recount the prosecution's criticisms. "You look at the discussion section of any medical study, and you'll find sentences like that: Needs more research. Needs a larger sample size. Needs to be replicated. Warrants caution. But it doesn't mean that what's been observed is wrong. It means that, as scientists, we're always cautious. Medical science is only ever proven true by history, but Amos Wells, from my point of view, had many genetic and neurological factors that impaired his mental ability. I say that not because I was a consultant to the defense, but in absolute terms."
Pietrini's point gets to the heart of a question still tackled by researchers and legal scholars: When do scientific findings become worthy of legal consideration?
The general assumption is that the same standards that guide the scientific community should guide the law, says Drexel University legal professor Adam Benforado, author of Unfair: The New Science of Criminal Injustice. "But I think that probably shouldn't be the case," he says. "I think when someone is facing the death penalty, they ought to have a right to present neuroscientific or genetic research findings that may not be entirely settled but are sound enough to be published in peer reviewed literature. Because at the end of the day, when someone's life is at stake, to wait for things to be absolutely settled is dangerous. The consequences of inaction are too grave."
That's basically the Supreme Court's stance, too. In the US, the bar for admissibility on mitigating evidence in death penalty proceedings is very low, owing to a Supreme Court ruling in the 1978 trial of Lockett against Ohio. "Essentially, the kitchen sink comes in. And in very few death penalty proceedings will the judge make a searching inquiry into relevance," says Morse, who begrudgingly agrees that neurobiological evidence should be admissible in capital cases, because so much is at stake. "I'd rather it wasn't, because I think it debases the legal process," he says, adding that most neuroscientific and genetic evidence introduced at capital proceedings has more rhetorical relevance than legal relevance.
"What they’re doing is making what I call the fundamental psycho-legal error. This is the belief that once you have found a partially causal explanation for a behavior, then the behavior must be excused altogether. All behavior has causes, including causes at the biological, psychological, and sociological level. But causation is not an excusing condition." If it were, Morse says, no one would be responsible for any behavior.
But that is not the world we live in. Today, in most cases, the law holds people responsible for their actions, not their predispositions. As Wells told his relatives in the courtroom after his sentence was handed down: "I did this. I'm an adult. Don't bear this burden. This burden is mine."
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