The suspect in the deadly attack in Toronto posted a Facebook message just minutes before a van ploughed into a crowded city pavement, authorities said, raising the possibility that he may have nursed grudges against women.
The 25-year-old suspect, Alek Minassian, was charged on Tuesday with first degree murder in the deaths of 10 pedestrians struck by the rented van. Fourteen others were injured.
Toronto Police Services Detective Sargeant Graham Gibson told a news conference that those killed and injured were "predominantly" women, though he declined to discuss a possible motive.
"All the lanes are open with this investigation," said Police Chief Mark Saunders.
Those known to have been killed include a 30-year-old woman from Toronto, Anne Marie D'Amico, who was active in volunteer work, as well as a female student at Seneca College, which Minassian also attended.
A family member identified one of the victims as 80-year-old grandmother Dorothy Sewell, who was an avid sports fan.
A Jordanian citizen and two South Koreans were also among those killed.
The gender issue arose because of what police called a "cryptic" Facebook message posted by Minassian just before the incident that suggested he was part of an online community angry over their inability to form relationships with women.
The now-deleted post saluted Elliot Rodger, a community college student who killed six people and wounded 13 in shooting and stabbing attacks near the University of California, Santa Barbara, in 2014.
Calling Rodger "the Supreme Gentleman," the Facebook post declared: "The Incel Rebellion has already begun! We will overthrow all the Chads and Stacys!"
Rodger had used the term "incel" - for involuntarily celibate - in online posts raging at women for rejecting him romantically. Like-minded people in internet forums sometimes use "Chad" and "Stacy" as dismissive slang for men and women with more robust sex lives.
Earlier, Minassian made a brief appearance in a Toronto courtroom in a white jumpsuit and handcuffs. The judge ordered him detained without bond and scheduled the next hearing for May 10.
Prime Minister Justin Trudeau dismissed the possibility of terrorism, saying that authorities see no national security element in the case.
He told a news conference that the incident "hasn't changed the overall threat level in Canada", though it occurred as Cabinet ministers from the G7 nations were meeting in Toronto.
Mr Saunders said Minassian, who lives in the Toronto suburb of Richmond Hill, had not been known to police previously.
"We are looking very strongly to what the exact motivation was for this particular incident to take place," Mr Saunders said. "We need every single piece of this puzzle so we can have a fulsome picture and account as to exactly what took place here."
The driver was heading south on busy Yonge Street around 1.30pm and the streets were crowded with people enjoying an unseasonably warm day when the van jumped on to the pavement.
Ali Shaker, who was driving near the van at the time, told Canadian broadcast outlet CP24 that the driver appeared to be moving deliberately through the crowd at more than 30mph, adding: "He just went on the sidewalk. He just started hitting everybody, man. He hit every single person on the sidewalk. Anybody in his way he would hit."
Witness Peter Kang told CTV News that the driver did not seem to make any effort to stop.
"If it was an accident he would have stopped," Mr Kang said. "But the person just went through the sidewalk. He could have stopped."
Video broadcast on several Canadian outlets showed police arresting the driver, dressed in dark clothes, after officers surrounded him and his rental Ryder van several blocks from where the incident occurred in the North York neighbourhood of northern Toronto.
He appeared to make some sort of gesture at the police with an object in his hand just before they ordered him to lie down on the ground and took him away.
Witness Phil Zullo said that he saw police arresting the suspect and people "strewn all over the road" where the incident occurred.
"I must have seen about five, six people being resuscitated by bystanders and by ambulance drivers," Mr Zullo said. "It was awful. Brutal."
Mr Trudeau on Monday expressed his sympathies for those involved.
"We should all feel safe walking in our cities and communities," he said. "We are monitoring this situation closely, and will continue working with our law enforcement partners around the country to ensure the safety and security of all Canadians."
The stretch of Yonge Street where the the people were struck remains closed to traffic and was expected to stay blocked off for several days as police continue what is likely to be a lengthy investigation.