PORTLAND — At the heart of Chad Gurney’s appeal to Maine’s highest court is the question of whether he understood what he was doing was wrong when he strangled Zoe Sarnacki, decapitated her corpse and set it on fire.

No one disputes that Gurney killed the former Deering High School student on Memorial Day 2009. He argued unsuccessfully during his two-week bench trial last year that he should be found not criminally responsible by reason of insanity.

Gurney, now 30, is serving a 60-year prison sentence for murder and arson. Had he been found not criminally responsible, Gurney would have been committed to a psychiatric facility until he was no longer considered a threat to society.

Gurney and Sarnacki, who was 18, had dated in the weeks leading up to May 25, 2009. After killing her that afternoon in his Cumberland Avenue apartment, Gurney had sex with her corpse, decapitated it, doused it with gasoline and set fire to it.

On Tuesday before the Maine Supreme Judicial Court, Gurney’s lawyer conceded that there is some evidence he understood the wrongfulness of his actions — but only after the fact. Other evidence, however, indicates that Gurney was not aware that what he was doing was wrong at the time, Sarah Churchill told the justices.

“That’s the time frame that’s really at issue here,” she said. “When he’s committing the acts against Ms. Sarnacki, what is going on in his mind?”

Gurney’s lawyers have argued that Gurney’s mental health was affected by a near-fatal van crash in 2005. Gurney suffered a brain injury, almost lost a leg and lost most of the use of an arm. The resulting seven-figure insurance settlement allowed him to live independently and to pay Sarnacki’s family more than $1.3 million to settle a wrongful-death lawsuit.

Testimony about how Gurney was changed by the accident, as well the role of personality disorder, the effect of medications and his sense that the universe was communicating to him through signs were among that factors that the trial judge needed to consider, Churchill argued.

“It’s all of those things in concert that make this case unique,” she said.

Chief Justice Leigh Saufley noted that the facts of the case strongly suggested that Sarnacki was the victim of domestic violence homicide. The prosecution had argued at trial that Gurney was angry that Sarnacki had been intimate with another man while he had been traveling.

One of the disputes in the appeal is about whether a reference on Gurney’s computer to a video about beheading a cheating woman should have been allowed. It was never determined whether Gurney had viewed the video.

Justice Ellen Gorman noted that there was evidence that could support either position and offered that a videotaped confession was possibly the most damning evidence against Gurney. Churchill disagreed with the trial judge’s assessment that Gurney was not delusional on the tape.

“Delusional thinking can still be present and you can still know the wrongfulness of your actions,” Gorman responded. “It’s not as simple as determining whether or not someone suffers from a mental illness … It’s your burden to establish that whatever major mental illness he was suffering form prevented him from understanding the wrongfulness of his actions at the time he killed her.”

Assistant Attorney General Donald Macomber said the evidence was overwhelming that Gurney knew what he was doing when he killed and decapitated Sarnacki and set the fire in the apartment.

Macomber said that evidence included Gurney instructing a friend to tell police he hadn’t been the same since his accident, his confession to police and evaluations of his mental state.

Macomber said Gurney’s story didn’t change until he got to Riverview Psychiatric Center in Augusta, where he was sent for an in-depth evaluation.

“All of the sudden he turned into a delusional person that was backed up by his $100,000 expert,” Macomber told the justices.

The justices did not indicate when they will issue their opinion in the case.

After the proceeding, Kathy Kosnow, Sarnacki’s aunt, compared hearing the details of her niece’s killing again to a puncture in the gut. But Kosnow tearfully explained why it was important for her to attend.

“To just be here for Zoe, to let her know that you care,” she said. “You don’t want to hear the stuff that’s said, but you have to. I think you have to.”