OTTAWA, Canada (CNN) -- A day after a gunman killed an army reservist in the Canadian capital of Ottawa, many questions remain.
Why did he shoot? Why did he target Nathan Cirillo? Is he connected to the militant group ISIS? Here's a list of what we know -- and don't know -- in the Ottawa shooting.
What we know: Canadian Prime Minister Stephen Harper called the attacker a "terrorist."
There have been troubling incidents in the nation recently.
The attack at Parliament and the National War Memorial Wednesday, which left Cirillo dead, was the second this week. On Monday, a man Canadian authorities said was a "radicalized" Muslim hit two soldiers with a car in Quebec, killing one of them. Police later killed the man.
Passports for the men in both attacks had been confiscated before they struck out at Canada's military. There was no immediate indication that the incidents were related.
But even before the two attacks, there was already concern about jihadist efforts in the nation. The United States heightened security at its Embassy in Ottawa as well as another consulate in the country after jihadist chatter indicated an attack could be in the works, according to officials.
What we don't know: The gunman's motive in Wednesday's shooting. With his death, the answer might never be fully known.
What we know: "We're satisfied at this point that one individual was responsible for the shooting yesterday on the hill," Ottawa police chief Charles Bordeleau told CNN partner CTV.
The alleged gunman was born Michael Joseph Hall in Canada in 1982, and changed his name to Michael Zehaf-Bibeau, authorities say.
The attack came two days after a "radicalized" Muslim man killed a soldier with his car, and five days after Canada raised its threat level.
What we don't know: Why he changed his name to Michael Zehaf-Bibeau, but two sources told CNN that he converted to Islam. While ISIS militants have stepped up recruitment efforts in Canada, there's no indication so far that the attacker was part of them.
What we know: Ottawa Mayor Jim Watson said the gunman was acting alone. "It appears there was just one shooter, and that shooter is dead," he said.
What we don't know: Whether he had any ties to any group or groups. A U.S. law enforcement official told CNN that a connection to terrorism hasn't been ruled out.
"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," said Prime Minister Harper.
What we know: Nathan Cirillo was the strong, smiling type. The Canadian army reservist could look the part of the intimidating soldier, but loved snuggling with his dog, enjoying music or joking with friends. He was part of the Argyll and Sutherland Highlanders, a reserve unit of the Canadian army.
What we don't know: Why the gunman shot Cirillo in the back -- "in cold blood," as Harper put it, while he stood guard at Canada's National War Memorial.
What we know: Kevin Vickers, sergeant-at-arms of Canada's House of Commons, is credited with bringing down the gunman. "Kevin is definitely a hero," said Matt Miller, the Vancouver Observer's parliamentary bureau chief, who was in his office just above the shooting.
What we don't know: Details on how he stopped the gunman. Several officers had weapons drawn, and most of the dozens of shots aimed at the gunman appeared to have been fired by officers. The Royal Canadian Mounted Police said more information would be provided in a news conference Thursday.
What we know: Shortly after the shooting at the memorial, a gunman entered the nearby building on Parliament Hill. 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.
What we don't know: Why the security agencies at the parliament did not tighten security after Ottawa police received a 911 call at nearby National War Memorial. We also don't know how the gunman slipped past the metal detectors and into the building.