Carney exchanged hugs and handshakes with other officials as he laid a bouquet at the base of an evergreen tree, near the school where a teacher and five young students were killed on Tuesday in the remote town of Tumbler Ridge, British Columbia.
The Liberal prime minister was joined by Conservative Party leader Pierre Poilievre, as well as leaders of smaller parties.
Jesse Van Rootselaar, 18, who had suffered a series of mental health problems, killed her mother and stepbrother at home before attacking her former school in Tumbler Ridge, a settlement of about 2400 in the Canadian Rockies, according to police.
Van Rootselaar, who police say was born a male but began identifying as a woman six years ago, then died by suicide.
Van Rootselaar was not targeting anyone specifically at the school, Royal Canadian Mounted Police Deputy Commissioner Dwayne McDonald said.
"This suspect was, for lack of a better term, hunting. They were prepared and engaging anybody and everybody they could come in contact with," he said at a news briefing.
The agency said earlier they had at one point seized guns from the house where Van Rootselaar was living but returned them after the owner, who they did not identify, successfully appealed the decision.
The Canadian Coalition for Firearm Rights, a pro-gun lobby group, questioned why weapons had been returned to a house where a person with mental illness was living.
McDonald said the two main weapons used in the attack had not previously been seized by police. He did not address the status of two other firearms that were used in the shooting.
The mass shooting was one of the worst in Canadian history. The deadliest took place in April 2020 when a 51-year-old man killed 22 people in Nova Scotia, before police shot him dead.
Few townspeople wanted to speak to media and British Columbia police said families and friends of the victims had requested privacy.
Police named the school victims as Abel Mwansa, 12; Ezekiel Schofield, 13; Kylie Smith, 12; Zoey Benoit, 12; and Ticaria Lampert, 12, as well as teacher Shannda Aviugana-Durand, 39.
Lampert's mother Sarah, speaking to reporters on Thursday, described her daughter as a "blazing light in the darkness ... (who) just wanted to bring sunshine to everyone and everything she ever touched."
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