Murder-suicide probe into highway horror of four dead

A 58-year-old male taxi driver and a mother and daughter, aged 56 and 81, died at the scene.

The SUV, which was recorded by its dashcam speeding in the moments before the crash, was engulfed in flames and its driver died at the scene.

The SUV's driver's speed and his decision to travel on the wrong side of the road into the path of oncoming traffic would be the focus of the investigation, Police Commissioner Col Blanch says.

WA Police Commissioner Col Blanch say a murder-suicide has not been ruled out. (Richard Wainwright/AAP PHOTOS)

"The investigation is focused on deliberate acts, if you will, being on the wrong side of the road and choosing to be there," he told 6PR radio on Tuesday.

Mr Blanch said police were investigating if the deliberate act was a murder-suicide, according to The West Australian newspaper.

"That's certainly part of the investigation and we may end up with that conclusion but it's too early to tell," he said.

The Commissioner said the crash was "really, really sad for all families involved".

"This is a horrific crash ... also for the first responders that attended that horrific scene ... probably something that would be burned in their memory for a long time," he told the radio station.

Salvaged dashcam footage from the burnt-out SUV shows the vehicle travelling east along Orrong Road, in Perth's east, before turning left and driving up the Leach Highway off-ramp on the wrong side of the road in a northerly direction towards the city's airport.

Detective Senior Sergeant Hugh Le Tessier said on Monday the driver had made a conscious decision to drive on the wrong side of the highway but it was unclear why.

"That's probably something we will never know," he said.