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 told CNN's Susan Candiotti. 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.Read it all here.
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.
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."
Cpl. Nathan Cirillo was killed after a gunman opened fire at the Canada War Memorial.