TORONTO -- The Conservatives tried to steer their campaign back to an old, faithful message on Tuesday as public opinion polls continue to suggest Stephen Harper may face the fight of his political career.

Harper, who has been asked repeated questions about the Mike Duffy scandal this week as his former chief of staff testifies in Ottawa, announced he will bring back a piece of tough-on-crime legislation if the Conservatives are re-elected.

The bill, known as "Life Means Life", was first introduced in March of this year but it died on the order paper when Harper opened the longest campaign in modern Canadian history.

For the first two weeks of the campaign, Harper has tried to hammer home his core message on the economy and security.

At an event in Toronto's Etobicoke-Centre riding, Harper turned up the volume on his tough-on-crime promises, suggesting Canadians expect to be protected from the worst type of criminals.

"Once this law is passed, criminals convicted of certain categories of first-degree murder will have no chance for parole, period," Harper said.

"I am talking here about the worst of the worst."

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

"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."

The original "Life Means Life" bill 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 -- who want the legislation brought back in its original form -- say it would address murders involving sexual assault, kidnapping, terrorism, the killing of police officers or corrections officers.

"Such convicts will spend the rest of their lives behind bars where they belong," Harper said.

"Quite frankly, any chance of freedom for such a perpetrator betrays Canadians' sense of justice and our faith in the justice system."

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

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.

"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.

Duffy eventually accepted $90,000 from Wright to repay his expense claims.

The disgraced senator has pleaded not guilty to 31 counts of fraud, breach of trust and bribery.