The Conservative government is developing legislation that would mean some murderers will have no hope of release from prison.

The new penalty would apply to several categories of those convicted of first-degree murder: killers of police and jail guards, anyone who kills during a sexual assault, kidnapping or act of terrorism and for especially brutal murders. The current penalty for first-degree murder is an automatic life sentence with the first chance for a parole review after 25 years, and the supervision of parole authorities for life.

The planned legislation has yet to be approved by cabinet, a source said. The departments of Public Safety and Justice, which are working together on the new bill, were told to speed up their work after a man shot two Mounties in St. Albert, Alta., on Jan. 17, killing one. The bill is expected to be introduced within a couple of weeks of a new terrorism bill coming on Friday, the source said.

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The change would reshape the Canadian legal landscape in an area seen as distinguishing this country from the United States. It sets the stage for the government's tough-on-crime policies to be a centrepiece of the federal election campaign expected next fall.

A spokesperson for Justice Minister Peter MacKay declined to comment directly on the categories outlined by The Globe, but quoted the Throne Speech of October, 2013, saying: "Canadians do not understand why the most dangerous criminals would ever be released from prison. We are currently reviewing options to ensure that a life sentence actually means life."

Prime Minister Stephen Harper attended the funeral in St. Albert on Monday of Constable David Wynn, his second such funeral in several months. In June, he was in Moncton for the funeral of three murdered Mounties. And in Ottawa, House Leader Peter Van Loan said the government will bring forward legislation this year "to ensure that a life sentence means just that, a sentence for life."

The United States is one of the last democracies with the death penalty, and all states but Alaska have the penalty of "life without parole." The U.S. Supreme Court says life without parole shares some characteristics with the death penalty in that it alters an offender's life by a "forfeiture that is irrevocable." Prisoner advocates have dubbed it "the other death penalty," and "death by incarceration."

Since Canada abolished the death penalty in 1976, the homicide rate has fallen from 3.08 victims for every 100,000 people to 1.44, its lowest rate since 1966.

"It is so patently a sentence that reeks of vengeance that it's hard to have a sensible political debate," Archie Kaiser, a specialist in criminal law at Dalhousie's Schulich School of Law in Halifax, said of life without parole. Vengeance is "really something we have cast aside in Canada, at least since we removed the death penalty."

Gary Clewley, a defence lawyer in Toronto whose clients are mostly police officers, said the law professor "confuses vengeance with legitimate public indignation. You can't compare a trial and appellate process at great public expense where people are guaranteed legal counsel and a trial of their peers to a lynch mob."

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If approved by Parliament, the new law could run afoul of constitutional rights, several legal experts said.

"The courts will take a very hard look at the proportionality of [continuing to imprison] a person who kills during a hostage taking in his 20s when he is in his 70s and 80s," University of Toronto law professor Kent Roach said.

Until now, the Conservative government has taken an incremental approach to life penalties. In 2011, it removed the "faint-hope clause," which allowed those convicted of murder to apply to a jury after 15 years for the right to an early parole hearing. Also in 2011, it allowed judges to add together the periods of parole eligibility for multiple murders. Two Canadians have been sentenced under the provision, including Justin Bourque, 24, sentenced to life with no eligibility for 75 years in the shooting deaths of three Mounties in New Brunswick last spring.

First-degree murder includes planned and deliberate killings and homicides that are not planned and deliberate but which happened during offences such as forcible confinement or sexual assault. All murders of police officers and jail guards are deemed first-degree. In brutal first-degree murders that compel the conclusion that the killer could not live by normal standards, a judge would have discretion in sentencing under the new legislation.

The cost could be enormous: Canada has 1,115 offenders who were sentenced to life for first-degree murder, of whom 203 have been released on parole; the average cost to keep a man in maximum security is $148,000, compared with $35,000 on parole, figures from Correctional Service Canada show. Forty years in jail would cost nearly $6-million for one person in maximum-security, and $6-billion for 1,000.

As of 2006, lifers on parole had killed 58 people. That category includes those such as Robert Bruce Moyes, sentenced to life as an armed bank robber, who, while on parole killed seven people in Abbotsford, B.C., in 1996.

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In recent years, the website of Correctional Service Canada has described those serving life sentences as "the most likely to succeed on parole." A spokesperson said on Monday the agency could not identify, for privacy reasons, the last first-degree murderer released on parole who killed again, nor how many have done so since 1976.