TORONTO (AP) — Police in London, Ontario, says a driver plowed a pickup truck into a family of five, killing four of them and seriously injuring the other in an attack that targeted the victims because they were Muslims.

Authorities say a young man was arrested in the parking lot of a nearby mall after the incident Sunday night.

Police say 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.

Twenty-year-old Nathaniel Veltman is in custody facing four counts of first-degree murder.

The Associated Press reported that Veltman, 20, who lived in London, did not know the victims.

Officials said it's early in the investigation to know if Veltman is a member of any specific hate group, but police are speaking with officials in London to see about potential terrorism charges, the AP reported.

The city's mayor says the incident "was an act of mass murder perpetuated against Muslims."

Flags will be lowered for three days in London, the mayor said.