OTTAWA -- A soldier gunned down while guarding a hallowed war memorial and a shootout in the halls of Parliament shocked Canada's capital and left parts of the city on lockdown for hours Wednesday.
Parliament member Kyle Seeback called it a "horrific day."
And it may not be over yet.
Authorities haven't ruled out the possibility that an additional shooter could be on the loose. And Ottawa Police Constable Chuck Benoit told CNN that there was more than one person involved in the shootings.
"We have to apprehend and arrest the people that are involved in this morning's incident," he said, "and at this time we don't have these people."
Michael Zehaf-Bibeau has been identified by Canadian officials to their American counterparts as the suspected gunman, multiple U.S. officials told CNN.
The gunman was killed after two shooting incidents -- one at the Canada War Memorial, and another just minutes later nearby inside Parliament.
Bibeau, who was born in 1982, was a convert to Islam and had a history of drug use before he converted, two sources said.
His passport had been confiscated by Canadian authorities when they learned he planned to go fight overseas, a U.S. law enforcement official said. The official said it was not clear when that happened.
Canadian broadcaster CBC reported that Bibeau had a record of drug arrests going back 10 years.
Authorities haven't specified whether the same shooter was involved in both shootings, and Canadian Prime Minister Stephen Harper didn't provide details about the investigation in a televised address to the nation Wednesday night.
Cpl. Nathan Cirillo was "murdered in cold blood," Harper said, expressing condolences to the slain Canadian soldier's family.
The soldier appeared to have been shot in the back, said Peter Henderson, a journalist who was at the memorial at the time of the shooting. Other soldiers who were nearby doing drills at the time ran to help, he said.
Henderson saw the soldier on the ground with "catastrophic" wounds.
Witnesses reported seeing the gunman run to the House of Commons firing dozens of rounds.
The Globe and Mail released cellphone video shot by one of their reporters showing a scene of utter chaos in the elegant hallway leading from the front doors of Parliament's Centre Block to the Library of Parliament during the attack.
MPs and other witnesses said they heard between 30 and 50 shots fired inside Parliament.
The gunman was eventually killed by the House of Commons sergeant-at-arms, according to the MPs' accounts.
Investigators haven't provided any possible motives for the shooting.
"In the days to come, we will learn more about the terrorist and any accomplices he may have had, but this week's events are a grim reminder that Canada is not immune to the types of terrorist attacks we have seen elsewhere in the world," Harper said. "Let there be no misunderstanding: We will not be intimidated. Canada will never be intimidated."
Three people brought to The Ottawa Hospital after the shootings have been released, hospital spokeswoman Hazel Harding told CNN. Earlier, they were described as being in stable condition.
Hours after gunshots thundered through the halls of Parliament, forcing people to barricade themselves in offices, police were still scouring the area.
Authorities lifted a safety perimeter in downtown Ottawa Wednesday night, but a police operation was still underway in Parliament Hill and a lockdown there remained in effect.
"If they thought that they had the situation under control, we would have been let out a long time ago. We haven't been. There's still no word on whether we will be," said Josh Wingrove, a reporter for the Globe and Mail newspaper who witnessed the shooting and remained at Parliament Wednesday evening. "This is by no means a situation that is considered over."
'I heard rapid fire'
Shortly after the shooting at the memorial, a gunman entered the nearby building on Parliament Hill, officials said.
"I heard rapid fire -- gunshots going very loud -- and I figure maybe 20-plus shots within 10 seconds," Canadian Deputy House Leader Kevin Lamoureux said. He was one level below the gunshots.
Gunfire first erupted in the building's foyer. Then a second round of shooting happened about a minute later in a hallway or near the entrance to the Parliament's library, Wingrove said.
Several officers had weapons drawn, he said, and most of the dozens of shots that he heard appeared to have been fired by officers at the gunman.
When the shooting ended, a person was lying motionless on the ground near the library entrance, Wingrove said.
Parliament member James Lunney tweeted: #HOC in Lockdown, lone gunman shot security guard, shot his way down Hall of Honor....we are all safe. Gunman dead! Thnk God & our scrty!"
In Twitter posts, several Canadian lawmakers hailed a top security official as a hero, crediting him with shooting the gunman inside Parliament.
"MPs and Hill staff owe their safety, even lives, to Sergeant at Arms Kevin Vickers who shot attacker just outside the MPs' caucus rooms," Craig Scott, a member of Parliament, wrote.
Another soldier killed Monday
Canadian authorities have given the name of a suspect to U.S. law enforcement and have asked for FBI assistance in tracing the person's activities, a senior U.S. law enforcement official told CNN. Only one name has been provided, and it is not clear whether the name is genuine or an alias, the official said. The official declined to provide more details, including the suspect's nationality, ethnicity and age.
A U.S. law enforcement official told CNN that a connection to terrorism hasn't been ruled out.
On Monday, a man who Canadian authorities said was "radicalized" killed a Canadian soldier with his car. The man was then shot and killed.
There was no immediate indication that the Monday and Wednesday incidents were related.
In response to the shootings, the North American Aerospace Defense Command, or NORAD, has increased its alert posture, CNN has learned. That means that it has increased the number of planes on a higher alert status ready to respond if needed. NORAD and Canadian authorities are in contact, an official told CNN.
Prime Minister secure during shooting
MP Tony Clement tweeted that he heard "at least 30 shots" and apparently was able to take cover with colleagues. He also tweeted that Prime Minister Harper was secure.
Harper was evacuated from the building and is safe, tweeted his press secretary, Carl Vallee.
Hours after the Parliament attack, Harper spoke by phone with U.S. President Barack Obama.
"Obviously, we're all shaken by it," Obama later told reporters, "but we're going to do everything we can to make sure we're standing side by side with Canada during this difficult time."
Ottawa Mayor Jim Watson said that Wednesday was "a sad and tragic day for our city and our country."
"There's no pain greater than losing a loved one -- to have it happen in such circumstances as this morning is beyond expression, and underlined by a sad anger within my heart," he said.
Canada raised its terror threat level
The violence at Parliament comes just days after Canada raised its terror alert Friday.
The suspect in Monday's vehicle attack, Martin Rouleau Couture, reportedly converted to Islam about a year ago. Police arrested him last July and confiscated his passport, but lacked enough evidence to keep him in custody, said Martine Fontaine of the Royal Canadian Mounted Police.
"When he was arrested, he was about to go to Turkey," Fontaine said. "We stopped him as he was about to leave Canada for terrorist actions. He was questioned when he was arrested. We have not been able to determine any real threat at this time."
CNN contributed to this report.