A woman killed in a serious head-on crash on Highway 6 in Hamilton may have been abducted or assaulted, police in Waterloo region say.

The woman was one of two people killed in the crash which happened as police were following the vehicle for more than 20 minutes.

According to Waterloo police Insp. Mike Haffner, officers were investigating a report of a possible abduction or assault of a female in Cambridge at around 9:30 a.m. when they attempted to stop a vehicle.

Haffner said the male driver of the vehicle did not stop for the officer and a pursuit began.

About 20 minutes later, the vehicle slammed into an oncoming transport truck on Highway 6 near Campbellville Road.

Both passengers, a man and a woman, were pronounced dead on the scene.

The driver of the transport truck was not injured.

Shortly after the crash, the province’s Special Investigations Unit was called in to investigate.

The SIU is called in to investigate any time police are involved in a death, serious injury or allegations of sexual assault.

OPP Sgt. Kerry Schmidt confirmed that there is “some police involvement” in the crash but could not provide any further details as the SIU has invoked its mandate.

Speaking to reporters from the scene, SIU spokesperson Monica Hudon said the vehicle was linked to an initial report about the assault of a woman but would not confirm if the woman had been abducted.

“That would be a part of our investigation. It’s still very early on,” she said.

Hudon also would not say whether police were in fact pursuing the car when it collided with the truck.

“Until we know this for a fact that this was a pursuit, I’m saying it was a ‘follow,’” she said.

“Our investigators are still attempting to identify the individuals and once I have information that I’m able to release, I will do so.”

Video from the scene shows a transport truck edged off the highway with a crumpled front end.

The second vehicle is scattered in pieces across the highway. A portion of the car appears to be crushed against the front of the transport truck.

OPP closed Highway 6 in both directions between Concession 10 and Campbellville Road for most of the day while they investigated.

The highway reopened shortly after 9:30 p.m.