A federal Conservative promise of tougher sentences for violent young offenders isn't endorsed by Merlin Nunn, the retired Supreme Court justice who led the inquiry into the death of a Halifax teacher's aide caused by a 16-year-old driver.

Nunn, whose work was cited as part of the basis of the Conservative platform, said he doesn't believe in long sentences.

"I think it's against the whole philosophy and thrust of the Youth Criminal Justice Act," he told CBC News on Tuesday.

Nunn said longer sentences wouldn't affect the majority of young offenders, who tend to commit only one crime and leave the justice system for good.

But they could have a dramatic effect on the approximately four per cent of young offenders who commit serious crimes, potentially turning them into career criminals, he said.

"I think they may be lost," Nunn said. "They won't be rehabilitated."

Harper should apologize, Liberal says

Under the party's election proposal, youth 14 and over found guilty of crimes such as manslaughter, murder or aggravated assault would face tougher sentences, and no longer have their identities protected.

The act currently forbids the release of young offenders' identities under most circumstances. Among those who can be identified are those handed adult sentences.

The Liberal camp weighed in on the issue with a call for Harper to explain why he "misled Canadians" by implying Nunn endorsed the Conservative proposal.

"First and foremost, Stephen Harper owes Justice Nunn an apology for grossly misrepresenting his recommendations," said Liberal justice critic Dominic LeBlanc, who is running in the New Brunswick riding of Beauséjour.

"Then he needs to come clean and admit his simplistic and ideological changes to the YCJA have absolutely no basis in fact and will do nothing to make our communities safer."

Goal is accountability, Tory candidate says

Conservative candidate Ted Larsen said the goal of the Conservative proposal is accountability for repeat violent offenders and greater protection for the public.

Prison can also help offenders with serious problems, he said.

"The fact of the matter is that the best place for them to be rehabilitated is within the correctional system, because that's the only place these programs exist — the proper mental health programs and other interventions," said Larsen, who's running in the riding of Halifax, where the fatal car crash occurred.

Nunn presided over the inquiry into the Oct. 14, 2004, death of Theresa McEvoy, a 52-year-old teacher's assistant and mother of three sons.

McEvoy was killed instantly when her car was broadsided by a speeding, stolen car driven by a 16-year-old boy high on drugs, who was wanted on two dozen charges at the time.

Archie Billard was convicted of criminal negligence causing death. In January 2006, he was handed an adult sentence of 4½ years in prison.