British Columbia, in western Canada, proclaimed Thursday a day of mourning across the province.
Five students aged 12 to 13 and a 39-year-old teacher were killed and at least 25 others were injured at Tumbler Ridge Secondary School.
Two others – the suspect’s mother, also 39, and 11-year-old step-brother – were found dead at a nearby home, where the attack began.
Two young victims remain in hospital in a critical but stable condition.
In Tumbler Ridge, flags remained at half-mast on Thursday, and a memorial to the victims was growing as mourners stopped by to drop off teddy bears and flowers and pause for a moment of silence.
Residents could be found hugging and comforting one another as they come to terms with what took place.
“Small towns are small towns. We look out for each other. It’s not like living in a city where you don’t know your neighbor,” said Shelley Quist.
“It doesn’t happen here. It doesn’t happen in Canada.”
Her son, Darian Quist, 17, was in the mechanics classroom with about 15 other students when the shooting took place. They blocked the doors and remained there for about two hours, until police escorted them out.
He said he knew one of the victims, and the students are feeling “all a little shocked, angry, sad, everything in between”.
That these attacks could happen in the first place, and “in a place like this, just doesn’t seem real”.
But he added: “I know people who lost their lives are real.”
On Wednesday, the Royal Canadian Mounted Police (RCMP) said there was a history of visiting Van Rootselaar’s family home in the past several years because of the suspect’s mental health struggles.
“On different occasions the suspect was apprehended for assessment and follow up,” said RCMP Deputy Commissioner Dwayne McDonald.
British Columbia Premier David Eby told a news conference outside the Tumbler Ridge town hall late on Wednesday evening they were in contact with the public healthcare system officials to “understand what interactions may have taken place”.
Van Rootselaar was born a biological male, but identified as a female, authorities said.
Tumbler Ridge has about 2,400 residents, and its secondary school, where the shooting unfolded, has 160 students. Police said Van Rootselaar had dropped out of school four years ago.
The RCMP also said there had been guns in the suspect’s home, which had been seized by police about two years ago.
Someone in the family, whom police did not name, later successfully petitioned to get the firearms back.
Authorities found two firearms – a long gun and a modified handgun – on the scene, though they said they did not know how the suspect procured the weapons used in the shooting.
A 2021 Facebook post from the suspect’s mother, Jennifer Strang, described how the teenager was interested in guns, BBC Verify found.
One post shared in 2021 by a relative shows the suspect holding a hunting rifle.