Stephen Harper tried once again on Tuesday to change the campaign channel back to a key issue for the Conservatives: getting tough-on-crime.

Harper, who has been peppered with questions on the Mike Duffy scandal this week as his former chief of staff testifies in Ottawa, promised that a re-elected Conservative government will bring back a "Life Means Life" bill that died when the election was called.

The Conservative government originally tabled the legislation in the spring.

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It proposed changing the Criminal Code to imprison offenders convicted of the "most heinous murders" and high treason for the rest of their natural lives.

The Conservatives say the bill would address murders involving sexual assault, kidnapping, terrorism, the killing of police officers or corrections offers.

At an event in Toronto's Etobicoke-Centre riding, Mr. Harper said Canadians expect to be protected from the worst type of criminals.

Sharon Rosenfeldt, who helped found the organization Victims of Violence after her son was killed by Clifford Olson, was on hand for the announcement.

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"When Clifford Olson murdered our son, we also received a life sentence," she told the crowd.

"It was not the state that was abducted, raped and murdered, it was my son."

Olson died in prison in 2011 and was never granted parole, but Rosenfeldt said the hearing process was "undeniably traumatic."

At an event in Sudbury, Ont., Liberal Leader Justin Trudeau said he is open to looking at proposals to better protect communities.

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But he said Harper was reintroducing the measure as a way to deflect attention from the Duffy trial.

Harper's Toronto event was interrupted after some Conservative supporters grew angry at journalists who were asking questions on the Duffy issue.

One man, who sat behind Harper during the event, barked out that reporters should ask questions "on the issue at hand."

Harper turned and raised his hand, urging the man to stop.

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"OK," he said.

Harper has only faced questions on the Duffy scandal this week. He continues to reiterate that Duffy and Nigel Wright, the former chief of staff, are being held accountable.

But evidence tabled in court shows that top insiders in the Prime Minister's Office were in on a secret plan to repay Duffy's expense claims while Canadians were told the senator repaid the money himself.