A mentally ill man who beheaded, and then cannibalized, a fellow passenger on a Greyhound bus last year cannot be held responsible for his actions, and will be housed indefinitely in a secure mental institution, a Canadian court ruled on Thursday.

Justice John Scurfield agreed with lawyers who said Vincent Weiguang Li, 40, was suffering from a major mental illness when he attacked a sleeping passenger on the bus in July last year, stabbing him dozens of times in the back and chest.

Li later held up the severed head of the victim, Tim McLean, and as police watched from outside the bus, he continued to mutilate the body and eat some of the remains.

Dr. Stanley Yaren, the only witness for the prosecution, had told the court that Li said he heard voices from God in his head telling him to kill McLean. He described Li as a "decent person" suffering from untreated schizophrenia, with a strong chance of recovery.

"He thought that Mr. McLean was an evil entity, that if he didn't kill Mr. McLean, Mr. McLean would kill him," said Li's lawyer, Alan Libman. "If Mr. Li, because of a mental illness, believed that he was defending himself, he didn't know what he was doing was wrong. And if someone doesn't know what they're doing is wrong, we don't punish them."

Debra Parkes, a law professor at University of Manitoba, noted that Li will stay indefinitely in a secure psychiatric hospital, subject to reviews, and this might give him a longer period in custody than a murderer sentenced to jail time.

The court also heard of a 2005 incident in which police picked Li up walking down an Ontario highway and Li said he was "following the sun." He was briefly hospitalized and given medication for schizophrenia, but he denied he had a problem and left the hospital.