CHICAGO (AP) — A jury has convicted the leader of an armed-robbery crew who prosecutors say terrorized store employees as they robbed retail stores in Chicago.

A Friday statement from the U.S. attorney's office in Chicago says 50-year-old Robert L. Berrios participated in nine robberies in 2012, mostly cellphone stores and currency exchanges. The Chicago man and his fellow robbers sometimes restrained store workers with zip ties as they collected hundreds of dollars in cash and phones.

Jurors returned Thursday with guilty verdicts on all 12 robbery, firearm and conspiracy charges.

Berrios faces a mandatory minimum prison sentence of 22 years. But his U.S. district judge has the option of imposing a life prison term when Berrios is sentenced on March 22. All four members of the crew charged have now been convicted.