First a soldier guarding a hallowed war memorial was gunned down in Canada's capital. Then shots erupted in the halls of the country's Parliament minutes later.
The two shootings in Ottawa Wednesday left lawmakers barricaded inside offices and parts of the city on lockdown for hours as police searched for suspects.
Ottawa Police lifted the lockdown Wednesday night and said there was no longer a danger to the public.
But many questions remain about the shootings: Who was the gunman? Why did he open fire? And was he acting alone?
"It appears there was just one shooter, and that shooter is dead," Ottawa Mayor Jim Watson told CNN's Anderson Cooper. "But it has been a traumatic experience, obviously, for not only our city but the country."
Investigators haven't provided any possible motives for the shooting. Canadian Prime Minister Stephen Harper didn't provide details about the investigation in a televised address to the nation Wednesday night.
"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."
It is unclear whether additional suspects were tied to the shootings or whether additional arrests have been made. The Royal Canadian Mounted Police said more information would be provided in a press conference Thursday.
As authorities continued to investigate, details began to emerge about the man they suspect was behind the shooting.
Michael Zehaf-Bibeau was identified by Canadian officials to their American counterparts as the suspected gunman, multiple U.S. officials told CNN.
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.
See more on this developing story on CNN.com