The Mounties who are assigned to protect him on a daily basis initially stood on the other side of the doors to that Parliamentary Reading Room, doors that suddenly seemed too thin, the locks too flimsy.
Already, RCMP Commissioner Bob Paulson has announced a change to Harper's security detail.
"Now we have adopted a condition where we will stay with the prime minister in his protective detail 24/7, no matter where he is," Paulson said at a news conference Thursday.
The dramatic accounts of what happened Wednesday morning on Parliament Hill continued to spill out in the aftermath, and have raised questions about the quality of safety in those marble and limestone halls.
MPs toured the hallway outside their caucus rooms Thursday, looking incredulously at the bullet holes left in the walls after the shootout between slain shooter Michael Zehaf Bibeau and House of Commons guards and RCMP officers.
In the case of the NDP's meeting space, the Railway Room, a bullet had passed directly through the main doors and into the padded, sound-blocking door behind it. There is another bullet hole in the wall outside the Conservative room.
The day began as most Wednesdays do when Parliament is sitting. Conservative and NDP MPs filed into their rooms on opposite sides of the Hall of Honour around 9:30 a.m. Often they give up their smart phones to uphold confidentiality.
A half-hour later, they heard a loud bang outside. Of the many MPs who spoke to The Canadian Press, all agreed that they thought nothing of that first loud sound — some thought it was food trays falling on the marble floor or the seemingly perpetual construction work outside.
Harper continued with his remarks to his caucus.
But then the rat-a-tat-tat of more gunfire boomed through the building.
The atmosphere in the caucus rooms changed radically. MPs described the sound as deafening. All said they thought several gunman were outside. The worst, say MPs, was the unknown.
"Because we heard so many gunshots, the impression I had was there were several gunmen outside with machine guns about to enter and spray the caucus," said Ontario Conservative MP Jay Aspin. "It was pretty traumatic."
"My next thought, was well, if they're right outside our door...the next thing they'd do is that there'd be a dozen terrorists busting through the wooden door and spraying bullets everywhere," said Treasury Board President Tony Clement.
Tables were overturned in the NDP caucus room.
"It never crossed my mind before, but wood doesn't stop bullets, why aren't these doors metal? And I wasn't so sure the locking was so great either — this feels precarious," MP Nathan Cullen said of his thought process. "If these guys are coming through, we're going to have to do something once they get through. Standing against the walls isn't going to cut it."
In both the NDP and Conservative rooms, unarmed House of Commons security guards who were able to get in helped to direct the parliamentarians and keep them away from the doors. Tories with military or police experience, such as David Wilks and Laurie Hawn, also helped to take control of the situation.
Several Conservatives said Harper initially tried to leave the room along with other MPs out of a north-facing door but was persuaded to stay instead of going out into the melee and an uncertain fate. Many Tories were initially convinced Harper had left, when in fact he was still in the room for about 15 minutes — hidden.
Harper hunkered down into what has been described as a closet or a closet-like space, according to multiple Conservatives. MPs and senators lay on the ground or stood pressed against the walls.
"We were told later that the decision was made to keep us in the room because the prime minister was there," said one Conservative, who spoke on condition of anonymity.
"So while we didn't know what was going on outside, the decision was made to keep in there."
Clement and colleagues Kyle Seeback, Mark Strahl, Michelle Rempel and Blake Richards made it out in the first moments and slipped up an adjacent stairwell, moving briefly towards the action.
"I thought where we were was going to be the murder zone so for me to get out of there made the most sense, although we ran right into the fusillade," said Clement.
Chairs and tables were stacked against the doorways. When an RCMP officer pleaded at the Conservative door to come inside, it took time for MPs to be reassured it was OK to open the entranceway and let him inside.
Harper was eventually whisked away once Mounties were let in the room. The rest of the caucus was left to wait in the room for another approximately nine hours, without food. Aspin, who is diabetic, says he luckily stocked his pockets with granola bars and a banana that morning.
Saskatchewan Conservative MP Randy Hoback said there was general feeling of confusion and helplessness.
"The first instinct was to get out of the room, but then you realize the firing is coming from outside the room so the best thing to do is stay in the room," said Hoback.
"I just basically went to the back of the room against the wall and sat down with a couple of colleagues, put my arm around them and said a little prayer and waited it out."
At one point in the day, House of Commons Sergeant-at-Arms Kevin Vickers came in with a blunt but comforting update.
"I engaged the assailant, he is deceased," Vickers told Conservative MPs, according to one who was in the room.
Clement and others who had barricaded themselves on another floor were eventually rescued by a soldier who had been busting down doors room by room through the building. They had to pass the doorway of the Library of Parliament, where the body of Zehaf Bibeau still lay.
The soldier moved them to a war memorial room on the third floor, where the MPs joined about 26 visiting students from Switzerland and a couple visiting from Texas.
Elsewhere in Centre Block, House of Commons and Senate staff were told to stay in their offices and lock the doors. When police did their rounds later, they entered rooms with guns drawn, ordering people to get their hands up and lie on the ground as they searched the area.
Democratic Reform Minister Pierre Poilievre was said to wield a bronze flagpole for most of the day, even clutching it hours later when they were escorted from the building.
By 10 p.m. on Wednesday, the precinct had been mostly cleared out.
A day later, MPs have many questions about the safety of their caucus rooms, the wisdom of leaving House of Commons security staff unarmed, and the security of the front doors to the building.
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