Four incidents have occurred within a two-month period " the most recent in Mandurah on Monday " and Detective Constable Shaun Leo said he believed they could be linked as three robberies targeted a Cash Converters, and in all four jewellery was stolen.
The escape vehicles used in two robberies were also found alight a short time later.
On Thursday, March 12, about 3.55pm, two men held up the Cash Converters on Warnbro Sound Avenue in Port Kennedy, with one man holding open a sliding door while the other smashed a glass cabinet and stole a large quantity of jewellery.
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READ NOWThey ran from the store and left in a green 4WD, which was driven by a third person.
The vehicle was located a short time later on Port Kennedy Drive and it had been set alight.
The second incident occurred on Monday about 9.45am at Cash Converters on Arnold Street in Mandurah.
One man entered the shop armed with a tomahawk and used it to smash a display cabinet, where he stole a large quantity of jewellery before running from the store and getting into a maroon Ford Falcon sedan.
The vehicle was discovered alight a short time later on nearby Anstruther Road.
Det Const Leo said the fact that large amounts of jewellery were stolen on all occasions and two cars were found burnt out was too much of a coincidence for them not to raise suspicions of being linked.
"We believe the same offenders have committed these robberies, certainly for the Mandurah one and in Port Kennedy," he said. "There's a little bit of time frame (between each incident) but they're similar, (with) the car burnt out, targeting jewellery and smashing glass cabinets."
He also said these two incidents may be linked to other armed robberies that targeted a jewellery store on Yirrigan Drive in Mirrabooka on March 3, and a Cash Converters on Albany Highway in Cannington on March 4.
Anyone with information i can call Crime Stoppers on 1800 333 000.