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Firefighters from the Lookout Point Fire Station quickly extinguished the fires, near a property in Isadore Rd, St Clair, after being alerted to them at 4.22am on Saturday.
There have also been several other suspicious fires involving parked cars in the city over the past month, including another vehicle in St Clair.
Asked if there were any links with other fires, Det Ferguson said police could not rule out a link and were keeping an open mind.
Fire Service investigators had ruled out any accidental mechanical cause for the fires in the Mitsubishi Triton double-cab four-wheel-drive utility and a 2003 Toyota Corolla car parked beside it, he said.
It is understood the two vehicles had a combined value of more than than $20,000.
The fires appeared to have been deliberately lit, he said in an interview.
He urged anyone who had seen any suspicious activity near this fire, or who had any information about any of the fires, to contact the police or to ring Crimestoppers on 0800-555-111, and provide the information anonymously.
The Saturday fire appeared to have been a random incident, and the two people whose vehicles had been destroyed were unaware of any possible motive.
Police were concerned about the fire and wanted to get to the bottom of it.
Both vehicle owners had worked hard to acquire their vehicles and it was clearly unacceptable the vehicles had been extensively damaged ''for no reason''.
Asked about the truck owner, Det Ferguson said he was a young man who used his vehicle for both work and recreation, and he had been ''devastated'' by its sudden loss.
Tools which he had kept in his truck had also been destroyed, and some other portable equipment had also been destroyed when the Toyota, parked nearby, had also gone on fire, he said.
The truck owner, a man in his 20s who had been away when the fire broke out, was later that morning still trying to come to terms with what had happened.
The truck owner asked not to be named, but said in an interview he used his truck for his work as a builder, and some of his tools, valued at several thousand dollars, had also been destroyed by the fire.
He had planned to be working on Saturday, but that had been made impossible with no tools or transport.
And he had hoped to go recreational hunting yesterday, but not being able to use his truck ruled that out.
The truck, which he had bought for $13,000, was covered by insurance, he said.
The Corolla was understood to be valued at more than $10,000.