The 20-year-old man allegedly took alcohol from Liquorland in Gwelup and BWS in Innaloo without attempting to pay.
Sergeant Cris Marzo from Scarborough Police station said the man took alcohol before showing the 20cm knife to the shop assistant at both incidents.
“He’s picked up some alcohol, walked out without paying and has been confronted before showing the shop assistant a knife that he had in his belt,” he said.
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READ NOW“He allegedly said ‘don’t follow me’ to the shop assistant while showing the knife.
“Response officers followed through with the CCTV footage and were able to identify a vehicle from a Clarkson home.
“Response officers did really well; it was a really timely response.”
A 40-year-old Clarkson woman who allegedly drove a getaway car for the man was also charged with robbery.
Detective First Class Constable Karen Higgs said a customer at the Innaloo shop noted the details of a vehicle the pair left in.
“Acting on that information, a search warrant was executed in Clarkson and a 20-year-old man was arrested,” Det Const Higgs said.
As well as the armed robberies, the man was also charged with breach of bail.
He appeared in Perth Magistrates Court last Saturday.