Strike Force Vulcan officers have appealed for witnesses to two separate suspicious fires in Rockingham and Waikiki to come forward.
The first fire was reported about 4.35pm on December 6 in a park surrounded by Santa Monica Drive, Bolsabay Drive, Ennis Avenue and Buttermere Approach in Waikiki.
The second fire was reported around 6.15pm the same day.
Emergency Services were called to a fire in bushland near the corner of Simpson Avenue and Louise Street in Rockingham.
Around 20 square metres of bushland was burnt.
Emergency services said both fires were suspicious and anyone with information to assist is asked to call Crime Stoppers on 1800 333 000 or make report online at www.crimestopperswa.com.au.
Rewards of up to $50,000 are available for information that leads to the identification and conviction of an arsonist.