The Conservative government will introduce life without parole for some killers, in what would be the biggest change to the Criminal Code since the abolition of capital punishment in 1976.

Prime Minister Stephen Harper said that, because of constitutional concerns, those sentenced to life without parole would have the right to petition the public safety minister, but not before 35 years have elapsed. The policy would revive a routine role for cabinet in release decisions that had ended in 1959 with the creation of the National Parole Board.

Life without parole, if approved by Parliament, would cap eight years of tougher crime laws that have contributed to record levels of federal prisoners, even as the murder rate has fallen to levels not seen since 1966. The policy would give a focal point to the national debate on crime and punishment as the country heads toward an election expected in October.

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Under current law, the first chance at full parole for first-degree murder is at 25 years. Mr. Harper, speaking in Toronto, said the government would remove parole for those who commit "especially brutal murders," those who kill during a sex assault, kidnapping or act of terrorism, and those who kill prison guards or police officers. The government will table the legislation in the House of Commons next week.

In the United States, roughly 40,000 prisoners are serving life without parole, including thousands sentenced as youths. The sentence applies to a variety of crimes, not just murder. "I think the big observation from the U.S. is this has been a slippery slope – it's gotten to be a major form of incarceration," said Richard Dieter, executive director of the Death Penalty Information Center in Washington.

Rick Sauvé, a lifer in Ontario who has been on parole since 1995, and who works with other lifers for the St. Leonard's Society, said he doubts inmates will receive a fair shake when they petition the public safety minister for release. "They would just act on emotion," he said of the minister. And "if you take all sense of hope, people can become desperate. It could create more violence in the prisons."

Legal observers called the 35-year review by the public safety minister a new "faint-hope clause" – an ironic reference to the 1976 law that gave convicted killers a chance after 15 years to apply to a jury for a chance at early parole. The Conservative government killed the 15-year review in 2011.

Several lawyers and academics interviewed said the 35-year review at the political level may not be enough to make life without parole pass muster with the courts. "I would say it's at least questionable," said Stephen Toope, a law professor and director of the Munk School of Global Affairs. "There will be an argument that this could amount to cruel and unusual punishment because of that sense of no hope." And giving the public safety minister control over release, he said, "might be seen as politicization of the sentencing function."

Mr. Harper stressed that violent crime committed by those with previous serious violence on their record is a betrayal of victims, and of the community.

"The suffering of the victims of such horrific crimes and the suffering of those who love them is bad enough," he said. "But what if, when the whole truth is known, they should find out that the crime could have been prevented in the first place, that the perpetrator was someone who could have been, should have been securely behind bars. When that is discovered, at that moment, their anguish is compounded by disbelief, and outrage, not just to them, but to the entire country, and then we are all left to wonder what justice means. They, we, feel betrayed."

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There are 203 people convicted of first-degree murder living in the community on parole, government records show. Mr. Harper cited no data on crimes committed by convicted first-degree murderers on parole. The Globe and Mail contacted the National Parole Board, Correctional Service Canada and the Canadian Centre for Justice Statistics, a branch of Statistics Canada. None said they had numbers available.

Sharon Rosenfeldt, a victims' advocate from Ontario whose son was murdered by serial killer Clifford Olson, praised the proposed changes. "Families who lose loved ones to killers like Clifford Olson will never have to attend parole hearings every two years," she said.

New Democrat MP Françoise Boivin, the party's justice critic, said that most dangerous killers are already denied parole. "Decisions about who is released should be based on the risk an individual poses to the community and how to best protect public safety."