Joel Reed used a crowbar and screwdriver to smash his way into a rear office within Monarch Coin Laundry on Mill Road on 24 March.
He ransacked the room looking for cash and made off with just £15 but as he was leaving the shop, two members of the public entered, and he pointed a knife at them.
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View all Peterborough Crown Court coverage
- Cambridge Arsonist Nabbed After Setting Christmas Decorations Ablaze
- Man Locked Up for Shocking Attacks
- Stalker Jailed for Fake 999 Call Claiming Ex-Partner Dead
- Church Volunteer Groomed Teen with 8,000 Inappropriate Messages
- Cambridge man jailed for vicious kidnap and robbery spree
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