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

Authorities said a young man was arrested in 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.”