David Tarloff lives in a deeply troubled inner world.

He was diagnosed as schizophrenic and hospitalized more than a dozen times before hacking a Manhattan psychologist to death with a meat cleaver. He has called himself the Messiah and was known to wander his apartment building half-clothed asking neighbors for money.

The 41-year-old Tarloff sat glassy-eyed in a courtroom last month after psychiatrists said he was mentally fit to stand trial on murder charges, though still prone to delusions.

His lawyer is pursuing a rare insanity defense in a case that highlights how the legal system tends to hold even severely mentally ill people accountable for answering criminal charges.

"Underlying our criminal justice system, there's this sense of personal accountability and responsibility. ... We're hesitant to relieve people of responsibility," said Richard E. Redding, a professor at Orange, Calif.-based Chapman University School of Law who has written on mental disorders and the law.

It wasn't clear that Tarloff — who sometimes refused to speak to his lawyer — ever would be considered competent for trial in the February 2008 slaying of Kathryn Faughey. He was sent to a state hospital a year ago for indefinite treatment before psychiatrists declared him fit for trial this fall. He is due for three days of further psychiatric examinations this week.

But the vast majority of people initially found unfit eventually are deemed competent, often after getting medication, Redding said.

The finding means Tarloff can understand such basics as the charges and his lawyer's role. His lawyer, Bryan Konoski, believes he has a strong bid for an insanity defense, which hinges on Tarloff's mental state at the time of the crime.

"Everything, about even how the crime took place, just screams insanity," Konoski said. "He had a thought process behind it, but it's an insane thought process."

Tarloff's disease emerged while he was a college student. He was hospitalized for the first time at 23. By 40, he was a bizarre and sometimes combative figure who despaired over his mother's move to a nursing home a few years before.

Eleven days before the slaying, he was arrested on charges of punching a security guard at a Queens hospital where his mother was being treated. A psychiatrist decided he didn't need further treatment, and he was released.

On Feb. 12, 2008, Tarloff set out to rob Dr. Kent Shinbach — his psychiatrist during his first hospitalization in 1991 — for money to whisk his mother out of the state, Tarloff later told police. He believed God had approved his plan, according to his lawyer.

Tarloff found Shinbach's office mate, Faughey, instead and slashed her 15 times. Then he attacked Shinbach and stole $90 from him when the psychiatrist tried to rescue her.

Tarloff later told his father he didn't know what had happened, police said.

But Faughey's family notes that Tarloff navigated the city and avoided detection for four days after the attack. Investigators ultimately matched his palm prints with some at the crime scene.

"I have a hard time believing he was completely nuts," one of Faughey's brothers, Mike, said this month.

Shinbach and Manhattan prosecutors declined to comment on the case.

While insanity defenses are a staple of crime dramas, they're uncommon in real life, offered for fewer than 1 percent of felonies nationwide and successful only about 20 percent of the time, Redding said.

The standards vary by state but generally require showing more than a serious psychiatric disorder. In many states, including New York, defendants must prove they didn't understand what they were doing or couldn't tell it was wrong.

Juries often are skeptical about the defendant's condition or struggle to draw a line between "mad and bad," Redding said.

In one noted case, a jury rejected an insanity defense for Andrew Goldstein, a schizophrenic who pushed a woman in front of a Manhattan subway train in 1999. Jurors later said they agreed he was mentally ill but felt he acted intentionally.

But some successful insanity defenses are notorious.

The defense worked for Lorena Bobbit, a Virginia woman who cut off her husband's penis in 1993, saying he was abusive. Some criticized the verdict as condoning crime in the name of compassion.

Congress and states around the country toughened laws after John Hinckley Jr.'s acquittal by reason of insanity in the 1981 shooting of President Ronald Reagan.

Some eliminated an alternative standard that allowed an insanity defense for conduct defendants knew was wrong but couldn't control.

Advocates for psychiatric patients rue that trend, saying narrower standards don't allow for the complexities of mental illness.

"We've never really figured out, as a society, how to deal with these kind of cases," said Ron Honberg, legal affairs director for the National Alliance on Mental Illness.

Tarloff faces life in prison if convicted. If found not guilty because of insanity, he'll be held in a mental institution until deemed fit for release, if ever.