Blame my brain: A killer’s bold defense gets a court hearing

He says his brain was coded to kill.

Anthony Blas Yepez didn’t deny beating an elderly man to death in Santa Fe, New Mexico, six years ago in a fit of rage. But after learning that he had a rare genetic abnormality linked to sudden violent outbursts, he argued for leniency, saying he wasn’t fully in control of himself when he committed the crime.

The claim seemed like a stretch to the judge, prosecutors and some scientists. But Yepez took it to the New Mexico Supreme Court, which agreed to consider it.

The court’s decision ─ still months away ─ could accelerate a trend in the criminal justice system: the use of behavioral genetics and other neuroscience research, including the analysis of tumors and chemical imbalances, to explain why criminals break the law. The rapidly developing field is forcing officials to confront new questions about how changes in the brain influence behavior — leading some to rethink notions about guilt and punishment.

This cutting-edge evidence, collected through brain scans, psychological exams and genetic sequencing, has been deployed in a range of ways: to challenge whether a defendant was capable of premeditated murder, whether a defendant was competent to stand trial, whether a defendant should be put to death. Most of those attempts to use neuroscience as a defense have failed, researchers say. But some ─ about 20 percent, according to one study ─ have worked, winning defendants new hearings or reversals.

That is troubling to researchers who fear some of the tactics push the boundaries of science.

“The law at the moment exists in this gray zone where everyone acknowledges that both genetic and environmental factors could affect culpability,” said Owen Jones, a Vanderbilt University law professor who directs the Research Network on Law and Neuroscience. “But how do you know when, and how much?”


Yepez’s journey to this frontier began with a mail-order DNA test.

In October 2012, he was charged with first-degree murder for beating to death the boyfriend of his girlfriend’s mother. He admitted to attacking the 75-year-old victim during a drunken dispute. But he said he could not remember much of it, and could not explain why he’d reacted so violently. He seemed bewildered at what he had done, according to Ian Loyd, a public defender who was assigned to represent him.

A few months later, as they prepared for trial, Loyd attended a conference in Washington. One of the speakers was forensic psychiatrist William Bernet. Bernet told the story of a Tennessee murder defendant, facing the possibility of the death penalty, who persuaded a jury in 2009 that he deserved a less severe punishment. The defendant had argued that a genetic deficiency — a variant of a gene named MAO-A, which regulates aggressive behavior in men — along with abuse he had suffered as a child were partly to blame for his crime.

The mutation’s impact on criminal behavior was first documented in 1993 in members of a Dutch family with a severe version that has since been found in a handful of families worldwide. There are less extreme, and less rare, versions that have been linked to an increased risk of criminal convictions — but only among men who also suffered from abuse as children. Some researchers began dubbing MAO-A the “warrior gene,” a term that was picked up by documentary filmmakerstalk show hosts and consumer-DNAtesting companies.

Loyd frantically scribbled notes, thinking of Yepez. “Maybe he’s got this gene too,” Loyd recalled thinking.

Loyd went online and found a commercial genetic testing company, FamilyTreeDNA, that charges $99 to determine if someone has the MAO-A deficiency. He had one of his investigators visit Yepez at the Santa Fe County jail, where he swabbed Yepez’s cheek for cells. A few weeks later, the results came back positive.

“This is the defense I want to pursue,” Loyd told Yepez.

Anthony Yepez
Anthony YepezNew Mexico Corrections Dept.

The consumer test wouldn’t hold up in court, so Loyd called Bernet, a professor emeritus at Vanderbilt University School of Medicine, who suggested getting a geneticist to perform a more comprehensive test. The geneticist, David Lightfoot, concluded that there was “no doubt” that Yepez had the MAO-A mutation, according to court filings. A psychologist also administered a series of tests on Yepez, who said he’d been mistreated as a child, including beatings with a belt buckle, according to Loyd.

A judge held a pretrial hearing in January 2015 to decide whether those findings could be used as evidence. A doctor testifying for the defense said the MAO-A deficiency and claims of abuse made Yepez “predisposed to committing violent behavior.” But prosecutors argued that the science was not reliable, and that the connection with the murder was weak. The judge refused to allow it.

Four months later, a jury ─ unaware of Yepez’s genetic mutation ─ convicted him of second-degree murder. The judge sentenced him to 22 years in prison.

Yepez appealed. A higher court said the judge should have allowed the genetic evidence, but did not overturn the verdict, saying it wouldn’t have made a difference because a second-degree murder conviction didn’t require showing Yepez had “specific intent” to kill his victim. Yepez appealed to the New Mexico Supreme Court, which agreed last fall to hear the case.

This article originally appeared on NBC