OTTAWA — The RCMP believes it has “come to a dead end” in its probe of where Parliament Hill shooter Michael Zehaf Bibeau got his gun — one of the most vexing questions about the events of Oct. 22, 2014.

The Mounties continue to investigate several threads of what happened that day, including whether Zehaf Bibeau had accomplices, but have not gathered evidence sufficient for criminal charges.

A source with direct knowledge of the police investigation provided the update to The Canadian Press on condition of anonymity due to the ongoing sensitivity of the file.

On Wednesday, crowds will gather for Remembrance Day ceremonies at the National War Memorial, where Zehaf Bibeau killed honour guard Cpl. Nathan Cirillo, shooting him in the back three times with a .30-30 Winchester rifle.

The attacker quickly made his way up Parliament Hill and into the Centre Block before being gunned down in the Hall of Honour, not far from then-prime minister Stephen Harper and many MPs.

The RCMP will honour 20 Mounties and former House of Commons security officers later this month in recognition of their bravery during the violent episode.

Shortly before his attack, the gunman made a video in which he cites retaliation for Canada’s military involvement in Afghanistan and Iraq as his motivation. Zehaf Bibeau, 32, plainly speaks of assaulting soldiers to show Canadians “that you’re not even safe in your own land, and you gotta be careful.”

RCMP Commissioner Bob Paulson told a Commons committee in March that the Mounties considered Zehaf Bibeau a terrorist, and that he would have been charged with terrorism offences under the Criminal Code had he lived.

Zehaf Bibeau became “increasingly aligned with terrorist ideology” in the last years of his life while living in the lower mainland of British Columbia and, for a short time, in Alberta, Paulson told the MPs.

“Anyone who aided him, abetted him, counselled him, facilitated his crimes or conspired with him is also, in our view, a terrorist and where the evidence exists we will charge them with terrorist offences.”

The RCMP had already devoted more than 130 full-time investigators and staff to the case, interviewing several hundred people across the country.

At the hearing, the commissioner said the RCMP was releasing a photo of Zehaf Bibeau’s gun, “which seems unique, in the hope that someone might recognize it.”

The lever-action, single-shot rifle was more suited to old Hollywood westerns than modern-day shooting sprees. But Zehaf Bibeau, who had a criminal record, would have been barred from buying a gun, and perhaps the Winchester was the only one he could get his hands on.

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The day before his attack, Zehaf Bibeau paid cash for a car that he drove to see his aunt in Mont-Tremblant, Que., where he was seen with a long knife. The knife was tied to his wrist when he was killed.

The Mounties suspect Zehaf Bibeau got his rifle “from a stash” he had at his aunt’s place. “We’ve been unable to conclusively establish this and we believe we’ve come to a dead end,” said the source familiar with the investigation.

It does not appear an accomplice, in the traditional sense, helped procure the gun for Zehaf Bibeau. RCMP investigators are pursuing “a number of threads of suspicious acquaintances and relationships” he had leading up to the attack, but the police force has not been able to conclude the ties amounted to “criminal liability” that could lead to charges, the source said.