The mother of a Manitoba man who was brutally killed on a Greyhound bus this summer says it is "not acceptable" that the man charged in her son's death could be found not criminally responsible, and be put in an institution rather than receive a prison sentence.

Carol De Delley, whose 22-year-old son, Tim McLean, was killed on a Greyhound bus near Portage la Prairie, Man., in July, is trying to raise awareness about the case. (CBC)In an exclusive interview with CBC News, Tim McLean's mother, Carol de Delley, said she's worried about the outcome of the case involving Vince Li, who has been charged with second-degree murder.

"The question has become: treatment or punishment? I think it needs to be both," she said.

McLean, a 22-year-old carnival worker, was on his way home from Alberta on July 30 when he was attacked as he slept on the bus near Portage la Prairie, Man.

Li, 40, was declared fit to stand trial earlier this week in a Manitoba courtroom. He remains in a Winnipeg hospital and is still undergoing psychiatric evaluation.

The trial will now largely depend on whether experts think Li was criminally responsible for his actions, defence lawyers said Monday.

Release 'a possible outcome'

A person found not criminally responsible is brought before the provincial mental health review board annually for an assessment. If the individual can prove to the board that he or she is no longer a risk to society, there is a possibility of eventual release.

Most people declared not criminally responsible spend much more time in psychiatric hospitals than they would if they were convicted of the same crime and given a sentence, said Debra Parkes, a professor of criminal and constitutional law at the University of Manitoba.

Tim McLean was on his way home from Alberta when he was attacked on July 30. (Family photo)Still, de Delley says if someone is found not criminally responsible, there should be no possibility — however remote — of future release.

"My goal at this point today is to raise the awareness that this is a possible outcome," she said.

"My reason for doing this is to make the public aware that under our current system, that is very likely what could happen unless we all speak up and say that this is not acceptable."

A candlelight vigil will be held on Oct. 16 at 6 p.m. CT at the Manitoba legislature in support of her family, de Delley said.

"I want as many people to stand behind my voice at that legislature to be heard by the people that make these changes. A change has to be made here. This is unacceptable," she said.

"[What] happened to my child was as brutal and gruesome as it was so that everybody would be paying attention. It was to wake everybody up."

Witnesses have said the attack on McLean appeared to be unprovoked — a man sitting next to him simply stood up and started stabbing him, then cut up his body.