Mounties received at least three warnings of potential terrorist attacks on uniformed officers before last year's shootings on Parliament Hill, yet the RCMP wound down extra patrols around the parliamentary precinct just days before the tragedy, newly disclosed documents show.

The RCMP unit that patrols Parliament Hill, which shooter Michael Zehaf-Bibeau, 32, successfully stormed, was understaffed by at least 29 positions at the time of the attack.

An inside glimpse of the RCMP's security posture on Oct. 22 is contained in a 1,000-page dossier obtained by CBC News under the Access to Information Act, following an 11-month delay in its release.

The file reveals an Oct. 18, 2014, "security reminder" from the force's Criminal Intelligence Integrated Unit, widely distributed the weekend before the shootings.

Cirillo Stevenson 3

Cpl. Nathan Cirillo, left, was gunned down while on sentry duty at the National War Memorial. The RCMP received at least three warnings in the days before the attack about potential terror-related violence. (Instagram)

The one-page warning said ISIS "is actively encouraging jihadists in the West and encouraging newly sworn militants to launch attacks against members of law enforcement from countries fighting its troops."

"ISIS threats against law enforcement in the West are real … Canada is not immune to such threats," read the document, which called on Mounties to take precautions, especially in their personal postings on social media.

A day earlier, on Oct. 17, the Integrated Terrorism Assessment Centre (ITAC), a multi-department unit hosted by the Canadian Security Intelligence Service, warned that a "violent act of terrorism could occur" and the centre increased the terror threat level that day to medium from low, where it had remained for four years.

The RCMP dossier shows the ITAC warning was widely distributed among Parliament Hill officers, who were specially told "to remain alert and vigilant."

3rd warning issued

Yet a third warning to RCMP officers was issued the day before the Ottawa shooting "outlining security/prevention measures for police officers with regard to recent threats made by the Islamic State group towards law enforcement." Details of the third warning, from the RCMP's National Intelligence Co-ordination Centre and which followed an Oct. 20 terror-linked attack in Quebec, were censored in the package released to CBC News.

The Harper government's 2012 deficit-fighting budget cuts had already seriously eroded staffing levels for the RCMP's parliamentary force. An October 2014 human resources report shows at least 29 vacant positions, and as many as 51 empty posts depending on the accounting method.

Michael Zehaf-Bibeau gun

This photo of the gun used by Michael Zehaf-Bibeau to kill Cpl. Nathan Cirillo was released by the RCMP at a House of Commons committee meeting on March 6.

There were a total of 177 positions authorized for the unit, but only 126 "members available," Supt. Luc Lemire reported to his bosses.

An Ontario Provincial Police investigation into the Oct. 22 shootings also cited the resource-starved RCMP unit, although the exact staffing shortfall numbers were blacked out in the public version of the final report.

The RCMP dossier shows that despite chronic staffing issues, the RCMP managed to increase its patrols in the parliamentary precinct and on Sussex Drive, near the residences of the prime minister and the Governor General, after two security incidents in mid-October.

'The approach to the security and protection of Parliament Hill is highly inadequate.' - Ontario Provincial Police report, March 2015

On Oct. 15, two men in a 2011 Ford Escape tried to force open the iron gates at Rideau Hall at 3:15 a.m. The next day, a man attempted to force his way into the Italian ambassador's limousine on Slater Street in downtown Ottawa.

Investigations later showed the first two men were drunk and harmless, and the latter was "mentally disturbed" and not a genuine threat. Even so, the RCMP launched "enhanced patrols" after the incidents — but stopped them on Oct. 20, two days before Zehaf-Bibeau's attack. He was shot dead after opening fire inside Centre Block on Parliament Hill.

The heavily censored public version of the OPP report from March 2015 does not refer to the terror warnings or increased patrols, but is highly critical of the minimal resources given to the RCMP.

Balkanized security

"The approach to the security and protection of Parliament Hill is highly inadequate," it concluded. "The RCMP posture on Parliament Hill has been challenging due to the limited amount of resources available, which are reflective of budget cuts in 2012."

The main solution, said the OPP report, was to unify the House of Commons and Senate security forces under the RCMP to provide seamless rather than balkanized security on the Hill. The government announced that very measure on Feb. 4 this year and the process of integration continues.

RCMP officials did not immediately respond to CBC News requests for comment on the security lapses.

Ottawa Shooting Nathan Cirillo memorial flowers

Floral tributes to Nathan Cirillo sit at the National War Memorial on the day after the corporal was shot and killed. A ceremony to mark one year since the incident is taking place at the memorial Thursday morning at 11 a.m. (Canadian Press)

Canadian Forces reservist Cpl. Nathan Cirillo was shot and killed as he performed sentry duty at the National War Memorial, and a House of Commons guard was wounded as he wrestled with Zehaf-Bibeau less than two minutes later inside Centre Block.

A commemoration ceremony is planned at the war memorial Thursday at 11 a.m. ET to mark the one-year anniversary of  the Ottawa attack, as well as the death of Warrant Officer Patrice Vincent from another terror-linked attack in Saint-Jean-sur-Richelieu, Que., on Oct. 20, 2014.

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