The case against a former Monterey college student accused of murdering his friend revolves not around whether he did it, but whether his mental illness was a key factor, a defense attorney said at the trial's start Tuesday.

James Torrey Hill, 24, is charged with fatally stabbing Matthew Finnigan, 26, after a night of drinking in Hill's apartment in 2010.

Defense attorney Michelle Wouden did not dispute that Hill killed his friend, but told jurors "what is in dispute is why this happened."

Hill's mental illness created "a perfect storm of tragedy," Wouden said. The case is "a map of a life with a broken compass," she said.

He had Asperger's syndrome, paranoia and cognitive and anxiety disorders, Wouden said, and his mental stability was "going downhill."

Hill told police he came from New Mexico to attend Monterey Peninsula College, where he and Finnigan took part in the College Living Experience, a private, off-campus program that provides housing and other services for young adults with special needs from learning disabilities to autism.

In a chilling videotape of Hill's police interviews the morning after the slaying, he said he needed to get "crazy drunk" the night of Sept. 22.

He explained that whenever he drank, demons appeared. The demons' voices, he said, urged him to satisfy a dream he'd had most of his life to kill someone before he died. That night, he said, he either had to kill himself or Finnigan.

He said the demons told him, "Sacrifice yourself or sacrifice someone else. Oh, just do it."

He slipped a kitchen knife into his sleeve and stabbed Finnigan once in the back as he lay on a mattress playing videogames.

A shocked Finnigan asked Hill to get his phone to call 911, but Hill told police he couldn't find it.

Hill said he didn't mind the delay, because he wanted to see Finnigan suffer.

Finnigan found his own phone and called 911. At one point, Hill got on the line and told the operator he probably had stabbed his friend.

Finnigan was airlifted to a Santa Clara County trauma center, where he died several hours later from internal bleeding.

In interviews at the Monterey police station, Hill appeared more than willing to cooperate, but also seemed coldly accepting of the fact that he'd just killed a friend.

Several times during his interviews, Hill said he tried to calm himself down that night, but then "the whole demon phase" took over.

"I'm sick of being harassed by all these demons," Hill told detective Jeremiah Ruttschow. "I'm too scared to ask for help. I didn't want to look weak."

Hill pointed to invisible points in front and behind him where he saw "a black, hooded floaty thing," adding that there were about 12 of them when he was drunk but only three the rest of the time.

"One says congratulations," he told Ruttschow. "One is shaking his head."

He recounted numerous suicide attempts over the years and admitted that about a month before Finnigan's slaying, Hill left his house carrying a hammer with the idea that he might kill a stranger. But he found it too difficult to gauge the possible reactions of strangers, he said.

He also said he had enjoyed "killing animals" when he worked at a veterinary hospital in New Mexico, where he helped euthanize pets.

He did not feel remorse, he said, even when Ruttschow told him his friend had died.

But Hill did say, "I wish I could have said something like 'Please go home. I'm going to be extremely violent with myself.'"

Prosecutor Doug Matheson downplayed Hill's mental state, saying he was "doing OK at MPC ... until his drinking catches up with him."

Stressing Hill's drinking as a bigger factor, Matheson said Hill had access to programs like Alcoholics Anonymous but "didn't like it. It didn't work."

He said Hill had the mental capacity to plan the stabbing in advance, go into his kitchen to get the knife and even hide it in his sleeve.

Wouden said she agreed with much of Matheson's description of the slaying itself, but said Hill did not harbor malice before stabbing Finnigan.

In the murder trial, which continues Thursday, "there are undisputed facts, but very highly disputed opinions or conclusions," Wouden said.