TORONTO (AP) — A driver plowed a pickup truck into a family of five, killing four of them and seriously injuring the other in a deliberate attack that targeted the victims because they were Muslims, Canadian police said Monday.

Authorities said a young man was arrested in the parking lot of a nearby mall after the incident Sunday night in the Ontario city of London. Police said a black pickup truck mounted a curb and struck the victims at an intersection.

“This was an act of mass murder perpetuated against Muslims,” Mayor Ed Holder said. “It was rooted in unspeakable hatred.”

Police said the dead were a 74-year-old woman, a 46-year-old man, a 44-year-old woman and a 15-year-old girl. A 9-year-old boy was reported in serious condition. The family requested the names not be released, officials said.

“In one act of murder some individual has wiped out three generations of family. It's horrific,” Holder said in an interview with The Associated Press.

Nathaniel Veltman, 20, was in custody facing four counts of first-degree murder. Police said Veltman, a resident of London, did not know the victims.

Detective Supt. Paul Waight said police did not know at this point if the suspect was a member of any specific hate group. He said London police are working with federal police and prosecutors to see about potential terrorism charges. He declined to detail evidence pointing to a possible hate crime, but said the attack was planned.

About a dozen police officers combed the area around the crash site looking for evidence Monday. Blue markers on the ground dotted the intersection.

“We believe the victims were targeted because of their Islamic faith,” Police Chief Stephen Williams said. “... There is no tolerance in this community who are motivated by hate target others with violence.”

Canada is generally welcoming toward immigrants and all religions, but in 2017 a French Canadian man known for far-right, nationalist views went on a shooting rampage at a Quebec City mosque that killed six people.

One woman who witnessed the aftermath of the deadly crash said she couldn’t stop thinking about the victims. Paige Martin said she was stopped at a red light around 8:30 p.m. when a large pickup roared past her. She said her car shook from the force.

"I was shaken up, thinking it was an erratic driver,″ Martin said.

Minutes later, she said, she came upon a gruesome, chaotic scene at an intersection near her home, with first responders running to help, a police officer performing chest compressions on one person and three other people lying on the ground. A few dozen people stood on the sidewalk and several drivers got out of their cars to help.

“I can’t get the sound of the screams out of my head,” Martin said.

From her apartment, Martin said she could see the scene and watched an official drape a sheet over one body about midnight. “My heart is just so broken for them,” she said.

Zahid Khan, a family friend, said the three generations among the dead were a grandmother, father, mother and teenage daughter. The family had immigrated from Pakistan 14 years ago and were dedicated, decent and generous members of the London Muslim Mosque, he said.

“They were just out for their walk that they would go out for every day," Khan said through tears near the site of the crash. “I just wanted to see.”

A fundraising webpage said the father was a physiotherapist and cricket enthusiast and his wife was working on a PhD in civil engineering at Western University in London. Their daughter was finishing ninth grade, and the grandmother was a “pillar” of the family, the page said.

Qazi Khalil said he saw the family on Thursday when they were out for their nightly walk. The families lived close to each other and would get together on holidays, he said.

“This has totally destroyed me from the inside,” Khalil said. “I can’t really come to the terms they were no longer here.”

The National Council of Canadian Muslims said Muslims in Canada have become all too familiar with the violence of Islamophobia. “This is a terrorist attack on Canadian soil, and should be treated as such,″ council head Mustafa Farooq said.

Nawaz Tahir, a London lawyer and Muslim community leader, said, “We must confront and stamp out Islamophobia and Islamic violence — not tomorrow, today, for the sake of our children, our family, our communities.”

The mayor said flags would be lowered for three days in London, which he said has 30,000 to 40,000 Muslims among its more than 400,000 residents.

“To the Muslim community in London and to Muslims across the country, know that we stand with you. Islamophobia has no place in any of our communities. This hate is insidious and despicable — and it must stop,” Prime Minister Justin Trudeau tweeted.