RCMP Commissioner Bob Paulson says he doesn’t know why four Mounties who helped corner and kill the Parliament Hill gunman one year ago were not invited to Thursday’s official commemoration.

“We have a troop of 32 people (who are) going to march in here, so I don’t know the answer to that question,” Paulson told CTV’s Ottawa Bureau Chief Robert Fife ahead of a sombre ceremony at the National War Memorial, where Cpl. Nathan Cirillo was killed.

Paulson has faced criticism after Sergeant-at-Arms Kevin Vickers was honoured for his part in subduing the gunman, while four heroic officers – including a man who delivered a shot killing Michael Zehaf-Bibeau – did not even receive a handshake or a thank you note from their boss.

Sources say the four officers had hoped that Paulson would invite them to Thursday’s ceremony.

Former RCMP Deputy Commissioner P.Y. Bourduas called the failure to include the men in the ceremony “a regrettable oversight.”

Paulson said, however, that he has publicly thanked his officers, and that a ceremony is being planned where the four Mounties will get commendations and bravery awards.

“Today is not the day to be talking about that,” he added. “Today is the day to be remembering what happened.”

Since the shooting, one of the officers was briefly assigned to RCMP car wash duty, sources say.

CTV News revealed earlier this month that an un-redacted copy of an OPP investigation showed that Const. Curtis Barrett, Const. Martin Fraser, Sgt. Rick Rozon and Corp. Dany Daigle helped corner Zehaf-Bibeau in the Centre Block on Oct, 22, 2014.

Barrett “could feel the percussion of (Zehaf-Bibeau’s) gunshot as he moved forward and then saw the barrel of the gunman’s rifle,” but continued “walking towards the gunman while firing,” according to the report. He fired 15 shots and remembers one shot “going into the gunman’s head.”

The OPP report said two bullets – including one in the brain -- were “rapidly fatal independently.”

Sergeant-at-Arms Kevin Vickers received a standing ovation in the House of Commons and an ambassadorship to Ireland after the world quickly learned he had likely fired one of the fatal bullets.

Sources told Fife the four officers were told two days after the shooting that “the Kevin Vickers train has left the station but you guys will get internal recognition,” including a commissioner’s commendation and recommendation for a Governor General’s Award – honours that never came.

In interviews on CTV’s Power Play Thursday, former Veterans Affairs Minister Erin O’Toole and outgoing NDP MP Megan Leslie recounted their experiences on the day of the attack. Both said they didn’t believe anyone was intentionally left out of the honours since there was so much chaos and confusion on Parliament Hill that day.

With a report from CTV’s Ottawa Bureau Chief Robert Fife