The Arson Squad have asked for assistance from the public regarding identifying a vehicle that was observed near the large Hazelmere bushfire around 1pm on Friday.
The vehicle is described as a white dual cab truck, and had concreting equipment including a cement mixer on board.
Three men were observed with the vehicle, believed to be wearing high visibility clothes with a concreting logo on them, and it is believed they could have information that will assist the investigation.
The fire got to approximately seven hectares in size and was a threat to nearby infrastructure before it was extinguished.
Arson investigators ask people with information regarding the men or the truck to call Crime Stoppers on 1800 333 000 or report the information online at www.crimestopperswa.com.au