The Ontario Provincial Police are taking over the investigation into a possible abduction and assault of a woman in Cambridge ahead of a fatal crash on Highway 6 Thursday morning.

Waterloo Regional Police tried to stop a red car after receiving a tip from a concerned citizen that a woman had been assaulted and forced into the car.

Officers attempted to pull the car over on King Street East in Cambridge, but the male driver fled and led police on a chase down Highway 401, then turned south on Highway 6.

The car crashed head-on with a transport truck at a curve in the road between Freelton Road and Concession 10, north of Hamilton. The man and the woman inside the vehicle died at the scene.

The transport truck driver and the police officers were not physically injured.

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Waterloo police said the investigation into the assault and abduction that led to the police chase remains open, but has been taken over by the OPP's major crimes unit. (Kate Bueckert/CBC)

'Devastating collision'

The crash scene was "horrific," OPP Sgt. Kerry Schmidt said at the scene Thursday.

"It is a devastating collision," he said. "It is a massive scene with horrific trauma to the vehicle, and the debris field is spread across a large stretch of the highway."

The Special Investigations Unit invoked its mandate to investigate the crash, because it may have involved police.

It is unclear if police were still in pursuit of the suspect vehicle at the time of the crash.

OPP 'better suited'

Insp. Michael Haffner said Friday the investigation into the assault and abduction that led to the police chase remains open, but has been taken over by the OPP's major crimes unit.

"We felt it was prudent as an organization to reach out to the Ontario Provincial Police as the Special Investigations Unit is conducting the collision investigation," Haffner said.

"We have the utmost confidence in our own members to conduct the investigation, but felt that — due to the circumstances — from an accountability and a transparency perspective an outside agency would better suited."

Focus on officer mental health

After Thursday's crash, officers spoke with SIU investigators at police .

The officers returned to the police service's south division offices in Cambridge, where they spoke with SIU investigators.

Haffner said the force is concerned about those officers's mental health.

"We do have a number of procedures and policies in place that address those circumstances," Haffner said. "This is tragic, not only for the community, but for our organization."