OAKLAND (CBS / AP) — A Northern California man has been convicted of participating in an elaborate jewelry robbery ring that used online ad service Craigslist to lure victims, prosecutors announced Friday.

The U.S. Department of Justice said that a federal jury in Oakland convicted Michael Anthony Martin, 42, of Tracy, of five counts of robbery. He faces a maximum sentence of 20 years in prison.

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Martin is one of five men charged with operating a ring that stole $500,000 worth of high-end jewelry from victims in six states during a one-year period ending in December 2013.

Martin’s attorney Paul Demeester didn’t return a call. Three of Martin’s alleged collaborators were previously convicted and received prison sentences ranging from 3 1/2 years to nearly six years. A fifth alleged member has pleaded not guilty and is awaiting trial.

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Prosecutors allege that crew members sometimes posed as music producers when contacting victims posting jewelry for sale on Craigslist. Other times, they would pose as young men in the market for engagement rings.

They allegedly purchased airplane tickets to fly some of their victims to the San Francisco Bay Area. Members would pose as airport limousine drivers and pick them up at airports, telling the victims they were being driven to a bank or jewelry store. Instead, prosecutors say the victims were driven to secluded areas and robbed at gunpoint. Some victims were pistol whipped.

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