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How do you crack a cold case? Try a cold case.

Nineteen Britons wanted on various crimes were arrested after being offered free beer by police in an undercover operation, according to Derbyshire (U.K.) Constabulary.

Dozens of suspects – for crimes including robbery and sexual assault — got letters from a marketing firm inviting them to call the company in exchange for a free case of beer, police said.

The calls were put through to officers at Chesterfield Police Station, who arranged a time to deliver the beer at the caller’s home, police said. At the appointed time and place, the caller was arrested.

“These suspects are people who have managed to evade arrest for some time, so we have used different tactics to find them,” said Chief Inspector Graham McLaughlin. “It has been very cost-effective, as it can take a lot of time and money to track people down.”

The operation was part of Operation Rocky, which targets “serious acquisitive crime across north Derbyshire,” a police statement said.