A 20-year-old man has been arrested for impaired driving following a fatal collision in Hamilton’s downtown core on Sunday evening that is also being investigated by the province’s police watchdog.

Hamilton police said they were attempting to stop a vehicle being operated by a suspected impaired driver when it collided with another vehicle on John Street, near Young Street, at around 11 p.m.

Two passengers in one of the vehicles died from their injuries, while the driver sustained serious but non-life-threatening injuries.

Police said the driver of the other vehicle was also transported to the hospital with non-life-threatening injuries and was later arrested for impaired operation causing death.

While Hamilton police’s collision reconstruction unit is investigating the cause of the collision, the Special Investigations Unit (SIU) is separately looking into the involvement of Hamilton police in the crash.

The SIU said there was an “interaction” between a Hamilton police officer and a man driving “erratically” before the collision.

Autopsies on the two victims are set to take place on Wednesday.

The SIU has assigned five investigators to the case.

The SIU is an arm’s length agency that investigates reports involving police, as well as special constables with the Niagara Parks Commission and peace officers with the Legislative Protective Service, where there has been death, serious injury, allegations of sexual assault, and/or where a firearm has been discharged at a person.

Anyone with information about this investigation, including dash cam footage, is asked to contact the lead investigator at 1-800-787-8529 or online at https://siu.on.ca/en/appeals.php.