OTTAWA -- Federal politicians, police forces and intelligence officials will begin the work of assessing security around Parliament Hill, and the safety of the country itself, in the wake of the shocking attacks in the nation's capital.

The Parliament buildings remained under close surveillance early today as the RCMP continued to sweep the area for evidence.

They are still piecing together the events that led to the fatal shooting of reservist Cpl. Nathan Cirillo on the steps of the nearby National War Memorial, and the burst of bullets that echoed later inside Parliament's Hall of Honour on Wednesday morning.

Michael Zehaf-Bibeau, born in 1982 and known to police in Montreal and Vancouver, has been identified as the gunman. He was killed just feet from where hundreds of MPs were meeting for their weekly caucus meetings.

Three other people injured in the melee were released from hospital Wednesday, including one person with a minor gunshot wound.

The shootings placed the heart of the national capital under lockdown throughout the day as police scoured the city's downtown core for other possible assailants. By Thursday morning, however, Ottawa police said they believed only one gunman was involved in the attacks.

Const. Marc Soucy said no other assailants were being sought, but added the investigation was ongoing.

A number of MPs -- some of whom showed up early today at the memorial to pay their respects -- declared their firm resolve to come right back to work today, even as police maintained a significant presence around Parliament Hill.

"Parliament will sit tomorrow at 10am as scheduled," Industry Minister James Moore tweeted Wednesday night. "Our democracy cannot and will not be intimidated by today's events."

The hill will remain closed to visitors, however, and the Speaker has announced a full investigation into House of Commons security.

As late as 9:30 at night -- almost 12 hours after the first shots were fired -- some MPs were still being evacuated after a long lockdown, and one government source said Bibeau's body was still lying in the hallway.

Early Thursday morning, a government statement said Ottawa police and the RCMP had lifted the downtown Ottawa safety perimeter and that federal public servants could now return to their offices.

Police say they do not yet know Bibeau's motive, but Prime Minister Stephen Harper has already drawn a link between his brazen actions and international terrorism. In a televised address late Wednesday, he said Canada would never be intimidated.

"In fact, this will lead us to strengthen our resolve and redouble our efforts and those of our national security agencies to take all necessary steps to identify and counter threats and keep Canada safe here at home, just as it will lead us to strengthen our resolve and redouble our efforts to work with our allies around the world and fight against the terrorist organizations who brutalize those in other countries with the hope of bringing their savagery to our shores," Harper said from an undisclosed location.

"They will have no safe haven."

What exactly a redoubling of efforts means will be addressed in the coming days.

Already, Canada has sent six fighter jets, surveillance and airlift assistance and 600 Canadian Forces personnel to fight the Islamic State of Iraq and the Levant (ISIL). In the last few weeks, there has also been heightened political scrutiny around Canada's ability to watch and apprehend radicalized Canadians who many have gone overseas and later returned.

But whether Bibeau is somehow linked to ISIL, or can be considered a radicalized Canadian, has not yet been established.

So many questions swirl around the attacks: How did Bibeau manage to get through the front doors of Parliament's Centre Block, and will security need to be permanently adjusted? Is he connected to any larger group that wishes Canada ill? Could someone have stopped Bibeau before he acted?

The fact that Bibeau struck only days after two Canadian soldiers in St-Jean-sur-Richelieu, Que. were hit by a car has only heightened the anxiety around the incident. The slain assailant, Martin Couture Rouleau, has been described as a radicalized Muslim.

Gen. Tom Lawson, the chief of the defence staff, issued a statement late Wednesday saying they are assessing the "current security environment and evaluating the need for additional security measures at Canadian Armed Forces installations..."

A fresh political debate is no doubt in the offing, but in the short-term the federal leaders were focused on condemning Bibeau's actions and rallying Canadians together.

"We woke up this morning in a country blessed by love, diversity and peace," NDP Leader Tom Mulcair said in a televised statement immediately following Harper's.

"And tomorrow we will do the same. These acts were driven by hatred but also designed to drive us to hate. They will not. We will stand up and we will stand together."

Already, there was a sense expressed by some that something had been irrevocably changed -- as it had after a man hijacked a bus 25 years ago and drove it on to the lawn of Parliament Hill, and after the Sept. 11 terror attacks in the United States.

Members of the public are required to use a specific entrance on Parliament Hill where there is a security screening area, but Bibeau apparently forced his way through the doors MPs, ministers, staff members and reporters are permitted to use.

"I think the intention was to try to make Parliament not look like Fort Knox," said Liberal MP Marc Garneau. "But we've crossed a river today."

Liberal Leader Justin Trudeau, meanwhile, sounded a note of caution.

"Criminals cannot and will not dictate to us how we act as a nation, how we govern ourselves and how we treat each other ... and they do not get to decide how we use our shared public places," Trudeau said in a late evening address.

Ottawa Mayor Jim Watson echoed the sentiment.

"I think we also have to ensure that we don't turn Parliament Hill into a fortress because that would send a signal that the terrorists and those who want to do harm to our system of government and way of life have won," said Watson.

Tales of Wednesday's dramatic events continue to spill out around Ottawa, a city that is more of a small town the closer one gets to Parliament Hill.

Trudeau had been heading down to a meeting on the basement level of Centre Block at the time of the shooting, but wound up being locked into his office for eight hours. Later, Trudeau and his staff were moved to an adjacent cafeteria as police went office-by-office through the six floors of the building.

NDP staff member Marc-Andre Viau was walking around the front door of Centre Block at 9:54 am, around the exact time Bibeau stormed through the doors.

"I saw someone in my peripheral vision rushing into Centre Block, through the main door...I can't describe him...I then turned my head and I saw a police officer chasing him," Viau recounted. "As soon as the police officer entered Centre Block, there were shots fired."

--With files from Joan Bryden