Judge rejects testimony that ‘warrior gene’ drove man to murder

Anthony Yepez, 26, is charged with choking and beating to death an elderly Santa Fe man, then soaking the man’s body in cooking oil and setting it on fire in October 2012. His defense team argued in a hearing Thursday that his genetic makeup, coupled with childhood abuse, predisposed him to impulsive violence. Phaedra Haywood/The New Mexican

Are some people more likely to commit violent acts because of genetic factors beyond their control?

Experts who testified Thursday during a preliminary hearing in a Santa Fe first-degree murder case said yes. However, a judge wasn’t so sure.

The witnesses said numerous studies have shown that people who have low levels of monoamine oxidase A, or MAOA — an enzyme that breaks down neurotransmitters including serotonin — are more likely to be impulsively aggressive, especially if these individuals were abused as children.

The testimony regarding a genetic makeup sometimes called the “warrior gene” was presented during a state District Court hearing on whether the condition can be used in the defense of Anthony Yepez, 26, who is charged with choking and beating to death an elderly Santa Fe man, then soaking the man’s body in cooking oil and setting it on fire in October 2012.

Yepez and his girlfriend, Jeannie Sandoval, were both arrested after George Ortiz, a 75-year-old relative of Sandoval with whom the couple lived, was found dead and burned in his apartment at the Luisa Senior Center. According to reports shortly after the killing, Sandoval told police that Ortiz had struck her in the throat during an argument and that Yepez had “intervened” on her behalf, choking and killing Ortiz.

Sandoval pleaded guilty to second-degree murder in June and was sentenced to nine years in prison with the understanding that she will testify at Yepez’s first-degree murder trial, scheduled to begin next week.

Assistant Public Defender Ian Loyd hoped to call three experts to testify at the trial that Yepez’s rare genetic makeup and maltreatment as a child made him more likely to act aggressively on impulse. Such testimony might help convince a jury that the killing wasn’t premeditated and open the possibility of conviction on a lesser offense, such as second-degree murder.

But prosecutors argued that the science behind the warrior gene is still too “young” to be relied upon — it’s only been used in one or two cases — and would only confuse the jury. Assistant District Attorney Susan Stinson also argued that too many other factors could have influenced Yepez’s behavior, and that his self-reported childhood abuse had not been corroborated by other sources.

District Judge Mary Marlowe Sommer on Thursday ruled in favor of the state’s request to exclude the experts’ testimony. She noted that the doctor who measured Yepez’s MAOA levels was not called to testify at the hearing, and that she still felt “iffy” about whether the science in the case was “reliable enough to prove what it proposes to prove.”

Loyd said not allowing the testimony would do an injustice to his client because it would keep his defense team from presenting Yepez’s main defense — if not his only defense. Loyd said Thursday that he’ll ask the judge to reconsider the ruling, and if she refuses, he will appeal the issue to the state Supreme Court.

“It’s our belief that [the judge] held the defendant to a burden of proof not required by any law or statute,” Loyd said, adding that under the rules that governed the hearing, the judge was only tasked with determining whether the scientific opinions were based on reliable facts and data.

Both witnesses who testified during Thursday’s hearing — Adrian Raine, a professor of criminology and psychiatry at the University of Pennsylvania, and James S. Walker, a Tennessee forensic neuropsychologist — said the correlation between low-activity MAOA and impulsive aggression is well documented.

“We’re as certain that MAOA is related to violence as we are that cholesterol is related to heart disease,” Walker said. “This is good science, done the way science is supposed to be done. I don’t know any serious behavioral scientist that disputes it.”

Walker said if he’s allowed to testify during the trial, he would give his opinion that Yepez’s history of childhood abuse combined with a low-functioning MAOA made him “exceptionally predisposed to commit violent behavior.”

Loyd said Yepez’s MAOA is about a 1 on a scale of 1 to 5, where 5 is considered normal.

Contact Phaedra Haywood at 986-3068 or phaywood@sfnewmexican.com.