CHICAGO (CBS) — The Chicago police union says an officer “inadvertently” shot an armed robbery suspect early Friday, after the suspect elbowed the officer in the chest in Canaryville.

Fraternal Order of Police Spokesman Pat Camden said it all started about 3:30 a.m., after three men robbed a man of cash and his iPhone at 21st and Wabash.

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Police were able to track the stolen iPhone to 43rd and Parnell, about three miles away, where police approached a vehicle, and tole the men inside to get out. An officer noticed one passenger was carrying a semiautomatic handgun with a 20-round magazine. That man elbowed an officer in the chest as he tried to get away.

“In doing that, the officer’s weapon fires, striking the offender, who did manage to get away. Dropped his gun at the scene, but he got away,” Camden said.

Police later found that suspect at Mercy Hospital, with a gunshot wound to the arm and chest. He was later transferred to Stroger Hospital, where he was listed in serious but stable condition.

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“When police tell you you’re under arrest, don’t resist – and the rest of the outcome will be fine,” Camden said.

Police said the other two suspects were arrested at the scene.

“The resistance of the offender caused him to get shot. On the bright side, we have three robbery offenders in custody,” Camden said.

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The Independent Police Review Authority was investigating the shooting.