WINNIPEG - He was an easygoing 22-year-old carnival worker who enjoyed hanging out with friends, playing video games and listening to the hard-core, hip-hop group Insane Clown Posse.

His attacker was a quiet, married man who immigrated from China in 2004, working a number of odd jobs including cleaning a Winnipeg church and delivering newspapers in Edmonton.

Their lives converged in an unspeakable act that shocked Canadians and made headlines around the world -- a quiet evening bus ride across the prairies that turned into a scene out of a horror movie.

One minute, Tim McLean was resting peacefully, listening to music through his earphones.

The next, passengers heard him "scream bloody murder" as he was stabbed over and over again, and eventually decapitated.

This coming March, Vince Li will go on trial in Winnipeg for second-degree murder before a judge alone. The only issue during the three-day trial will be Li's state of mind.

The legacy of the unprovoked attack is still being felt -- from new metal detectors in major Canadian bus stations to a call for tougher legislation for mentally ill people found not criminally responsible for their actions.

"I think this case strikes a chord with Canadians and upsets Canadians," said Alan Libman, one of Li's lawyers.

"It just shows us how fragile and unpredictable life is. This poor young man did nothing wrong. This poor young man and Mr. Li had never met, had no prior relationship. It just shows how uncontrollable the circumstances of life can be."

Li's lawyers are not disputing that he killed McLean.

The evening bus ride began uneventfully, that night back in July.

McLean was heading home to Manitoba after working at an Alberta fair. He chose a seat near the back of the bus. The bus stopped at a rest stop and McLean made small talk with fellow passengers as they had a smoke.

As the bus carried on toward Portage La Prairie, Li moved from his perch at the front of the bus to the back and took a seat next to McLean. A movie played to pass the time. McLean listened to music on his earphones and texted an old girlfriend before closing his eyes and resting his head against the window.

"We heard this blood-curdling scream and turned around, and the guy was standing up, stabbing this guy repeatedly like 40 or 50 times," remembered fellow passenger Garnet Caton.

"There was no rage or anything. He was just like a robot, stabbing the guy."

Passengers rushed to the front, telling the driver to pull over. They scrambled to get out while the attacker started methodically carving up McLean's body, ignoring the chaos around him.

Caton and the driver barred the door from the outside while they waited for police.

Christopher Alguire was driving his truck along the highway, hauling a load of metal pipe from Alberta, when he saw passengers running from the bus parked on the side of the road. He pulled over and grabbed a metal bar from his truck.

Alongside a driver from another Greyhound bus that had pulled over, Alguire went into the bus to ensure no other passengers were on board. He watched a man leaning over McLean's body, hacking at his neck with a knife.

His eyes were "empty," Alguire remembered.

"It was like staring into a black hole."

Alguire followed the driver off the bus and bolted the door.

"The guy came to the front of the door with buddy's head in his hands, decapitated," remembered passenger Cody Olmstead, from Kentville, N.S.

Olmstead had just shared a cigarette with McLean hours before.

"He dropped the head and went back and started cutting the body back up."

Caton remembers throwing up at that point.

"He was wearing sunglasses," Caton said of the attacker. "It was no big deal to him."

The attacker turned away, sitting in the driver's seat and tried to start the bus, but the engine was disabled.

Police tactical teams arrived and arrested the suspect when he tried to climb out a bus window. Crown prosecutors say police then discovered a plastic bag containing an ear, nose and part of a mouth in the pocket of the accused.

Since then, very few have seen Li. He appeared in court in Portage La Prairie a few days after the gruesome killing, and just shook his head when asked if he wanted a lawyer.

"Please kill me," he said quietly.

His trial was moved to Winnipeg, where all spectators have to pass through airport-like security, following threats made on Li's life.

None of those who witnessed the horror that night will be expected to relive the experience at Li's trial. An agreed statement of facts will take care of the details of the attack.

Instead, the witnesses are expected to consist mainly of forensic psychiatrists who can speak about Li's mental health.

"The defence or Crown can raise evidence that the person didn't have the requisite mental intent, he didn't have any malice," Libman said. "In this type of situation, it would be that the person didn't know that killing that person was wrong, either morally or legally . . . There was no attempt to conceal it, no attempt to run away."

If Li is found not criminally responsible, he could be immediately discharged by the judge or hospitalized indefinitely depending on the seriousness of the crime. If he is ordered to undergo treatment, he would be reassessed regularly by a mental health review board.

"We don't punish people if they didn't intend to do something or if they honestly believed what they were doing was right because of an illness," Libman said. "We don't punish people who are not at fault. He would just be treated and get medical help."

But for Carol deDelley, McLean's mother, the prospect that the man charged in her son's death might eventually be released is too much to bear. She, along with others, are already pushing for tougher laws to ensure that doesn't happen.

"My son Timothy lost his life and our lives will never be the same without him being a part of it," she said at a recent vigil to press for changes to legislation. "Myself and my family are seeking justice for Timothy (and) mercy for ourselves."

The family is also suing Greyhound, the federal government and Li for failing to ensure McLean's safety. The $150,000 lawsuit is not about the money but is about accountability, the family's lawyer has said.

In the meantime, Greyhound has brought in increased security at some major bus stations. Passengers in Edmonton, Winnipeg and Calgary will now be swept with hand-held metal detectors before they board the bus. But most bus stops are in small towns or by the side of a rural road where passengers won't be screened.

However, all passengers have to stow their luggage in the cargo compartments with the exception of purses, wallets and books.

Other bus companies have taken it one step further.

The Saskatchewan Transportation Company, which runs bus service across the province, just brought in new security measures including cameras, global positioning units and a panic button that immediately dispatches police to the bus's location.

Drivers are also getting more training in self-defence and conflict resolution.

Although Greyhound said they still "have a lot of full buses," spokeswoman Abby Wambaugh said they won't be assessing ridership until early January.

"It was a very tragic event that occurred in Manitoba and not one that we believe we could have been prepared for," she said.