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Killer’s Bold DNA-Based Defense to Get New Mexico Supreme Court Hearing

by Bill Barton

Anthony Blas Yepez, in October 2012, beat to death the 75-year-old boyfriend of his girlfriend’s mother in a drunken dispute. Charged with first-degree murder, Yepez said he could not remember much of the incident and didn’t know why his reaction was so violent. Public defender Ian Loyd, who was assigned to represent him, said, “He seemed bewildered at what he had done.”

While preparing for trial, Loyd learned about the existence of a variant of MAO-A, a genetic mutation that affects the regulation of aggressive behavior in men, from forensic psychiatrist William Bernet, who spoke at a conference in Washington that Loyd attended.

The mutation was first documented in 1993 in a Dutch family, and some researchers dubbed it “the warrior gene,” according to the NBC News story about Yepez. “Maybe he’s got this gene, too,” Loyd recalled thinking.

Loyd went online and found a commercial genetic testing company, FamilyTreeDNA, that charged $99 to check for the MAO-A deficiency. After an associate visited Yepez in Santa Fe County jail and swabbed his cheek, the DNA sample was sent in. A few weeks later, the results came back positive. “This is the defense I want to pursue,” Loyd told Yepez.

When the consumer DNA test wouldn’t hold up in court, Bernet was consulted and advised Loyd to get a geneticist to perform a “more comprehensive test.”

David Lightfoot, the geneticist, concluded that there was “no doubt” that Yepez had the MAO-A mutation, according to court filings. And, according to Loyd, “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.”

This type of childhood abuse was mentioned as key to the worsening of the mutation that linked to an increased risk of criminal behavior.

The judge refused to allow the MAO-A testimony, and four months later, a jury convicted Yepez of second-degree murder. He was sentenced to 22 years in prison. He appealed. The appellate court ruled that the judge should have allowed the genetic evidence but did not overturn the verdict. Yepez subsequently appealed to the New Mexico Supreme Court. His case remains pending as of the publication of this article.

Helen Bennett, the attorney representing Yepez before the state Supreme Court, said, “These genetic markers and the way we’re learning how they operate in the brain makes the determination of intent much more nuanced.”

Nita Farahany, a professor at Duke University, wrote in the January 2019 Annual Review of Criminology, that “Year after year, more and more criminal defendants are using neuroscience to bolster their claims of decreased responsibility for their criminal conduct and moral culpability relevant to their sentencing.”

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

Henry Greely, director of the Center for Law and the Biosciences at Stanford Law School, said that if he were a judge in Yepez’s case, he probably would not allow the MAO-A evidence. “It’s not going as far as junk science, but it’s close,” he said.

Bennett, however, said, “We have a duty as citizens to listen to that science and make informed decisions before we take away another person’s freedom.” 



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