A 49-year-old man walked 2km from his crashed car before he died by a Wheatbelt roadside at the weekend, police believe.
Major Crash investigators are appealing for information from the public about the death of Louis Athan in the early hours of Sunday morning.
Mr Athan was driving his dark grey coloured 2011 HSV (Holden) GTS sedan on the Newdegate-Ravensthorpe Road when he crashed into trees near the Old Ravensthorpe Road intersection.
Police believe Mr Athan walked about two kilometres towards the Newdegate town.
Investigators have established that Mr Athan's fatal injuries "involved two vehicles".
A small passenger vehicle which had been identified and a larger vehicle, probably a heavy truck, were involved.
Police say it is possible the driver of the larger vehicle was unaware of the incident.
Investigators are trying to identify any large trucks in single, road train or B-double configuration that drove along the Newdegate-Ravensthorpe Road between 1.30am and 6.30am on Sunday, March 30.
Anyone with any information should call Crime Stoppers on 1800 333 000.