(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.
THE SHOOTER:
What we know: The alleged gunman was born Michael Joseph Hall in Canada, and changed his name to Michael Zehaf-Bibeau, authorities say. He was 32 years old according to court documents.
He was a Canadian citizen who may have had dual Libyan citizenship as well, Royal Canadian Mounted Police Commissioner Bob Paulson said.
Zehaf-Bibeau had criminal records indicating infractions related to drugs, violence and other criminal activities, police said.
His father is a Quebec businessman and his mother works in Canada's Immigration and Refugee Board, according to the Globe and Mail newspaper. The parents are divorced.
What we don't know: Why he changed his name, 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.
THE MOTIVE:
What we know: Authorities said Zehaf-Bibeau had been applying for a passport and hoped to travel to Syria. His passport had not been revoked, as earlier stories have said.
"I think the passport figured prominently in his motives," Paulson said. "However, we have not come to ground completely on his motivations for this attack. But clearly, it's linked to his radicalization."
Was Zehaf-Bibeau a jihadist? He had "connections" to jihadists in Canada who shared a radical Islamist ideology, including at least one who went overseas to fight in Syria, multiple U.S. sources told CNN.
But Canadian Foreign Minister John Baird said there is "no evidence at this stage" he was linked to jihadists.
What we don't know: The motive. And with the gunman's death, it may never be known.
ACCOMPLICES:
What we know: Ottawa Mayor Jim Watson said thegunman 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.
"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," Prime Minister Stephen Harper said.
THE VICTIM:
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.
His uncle, Jim Cirillo, told CBC News that his father is in Costa Rica and might not yet know about his son's death.
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'sNational War Memorial.
THE HERO
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 SECURITY:
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.
Another disturbing incident occurred Thursday. As the Prime Minister and his wife laid a wreath in memory of Cirillo, a man yelled and wrapped a white scarf around his face. Police quickly subdued him.
What we don't know: Why the security agencies at the Parliamentdid 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.