Carol deDelley, whose son Tim McLean was decapitated while riding a bus, wants anyone who commits a crime to be punished regardless of whether they were mentally ill at the time or not. (CBC)

A high-profile murder trial that begins in Winnipeg this week has reignited debate about whether people with mental illness should be treated or punished when they commit a crime.

The trial for Vincent Li, accused of decapitating 22-year-old Timothy McLean on a Greyhound bus in Manitoba last July, begins Tuesday and is set to last all week. It has been widely reported that the Crown prosecutor and defence attorneys will likely argue Li is not criminally responsible for his actions.

"We're going into this trial knowing that it's very likely that Mr. Li will receive NCR [a ruling of not criminally responsible]," Tim McLean's mother, Carol deDelley, told CBC Monday.

Wearing a T-shirt with the slogan "Tim's Law," referring to the victim-protection legislation she has been advocating for, and her son's St. Christopher medal — which McLean was wearing the day he died — deDelley expressed her adamant opposition to what she saw as the leniency granted to people found not criminally responsible.

The finding would mean Li would be sent to a federal psychiatric facility rather than a prison. If he successfully completed treatment, Li could be eligible for discharge and released back into the community. That decision rests with the court or provincial review board.

"It also means no criminal record, which is something I don't think the public is really very well aware of," said deDelley.

She said she believes anyone found not criminally responsible for their actions should remain inside a treatment facility for the rest of his or her life.

"If you voluntarily take an innocent life … you forfeit your freedom. That's the cost of it," she said. "I don't think that having a mental illness absolves people of their responsibilities for their actions. I just don't believe that."

'It's kind of fundamental to our criminal law to have some different way of treating someone who simply does not have the ability to understand … what they're doing due to a mental disorder.'—Debra Parkes, University of Manitoba

That option is an important part of the justice system, said Debra Parkes, a professor at the University of Manitoba's faculty of law.

"It's kind of fundamental to our criminal law to have some different way of treating someone who simply does not have the ability to understand … what they're doing due to a mental disorder, or of knowing it was wrong," she said.

However, family and many other families of murder victims across Canada have argued that approach is not right or just.

Ann Tavares's son Steven was stabbed 28 times by a co-worker on Nov. 7, 2004, just outside of Calgary. The accused killer was found not criminally responsible based on evidence from three psychiatrists, who all agreed he was mentally ill.

Less than three years later, the Alberta Review Board allowed his conditional release from custody, though he remains under the board's authority. He is now living and working in Edmonton.

"OK, if it takes you three to four years to be treated and the hospital says you're fine and discharged, you should finish the rest of your sentence in a prison," said Tavares.

Changes to Criminal Code being pursued by victims' families

Tim McLean's family has been lobbying for changes to the Criminal Code, pushing for victim-protection legislation they call "Tim's law."

The proposed legislation would prevent a person found not criminally responsible of a crime from being released into the community. It would mean that the most violent, unpredictable people who have committed a crime would face incarceration for life, with no possibility of parole.

"Tim's Law means life, which means if you take a life, you receive a life sentence. And by a life sentence, I mean the rest of that criminal's natural life," deDelley told CBC. "If [Li is proven to be] mentally ill, then he has a life sentence in a locked facility. I just don't think that we can put him back out in the public.

'I don't want him ever free, to ever be able to repeat this behaviour and devastate another family.'— Carol deDelley

"If he's fine [when he's]medicated, great. But keep him behind locked bars for the rest of his days so the rest of us are safe.

"I don't want him ever free, to ever be able to repeat this behaviour and devastate another family."

Jennifer Chambers, a mental health advocate in Toronto, understands the emotional reaction by victims' families, but says the belief that a finding of not criminally responsible is not a type of punishment is flawed.

"It's based on a misunderstanding, in part from watching American TV, that getting found not criminally responsible is somehow getting off. But also, it's based on the concept that vengeance is always the right response to someone who's committed harm," she said.

"In fact, if you're found [not criminally responsible], you usually spend much longer in custody than if you were found guilty of crime, so in that respect, if people are looking for punishment, people usually get more punishment than they typically deserve."