Chicago police caught an armed robbery suspect carrying an automatic pistol in the South Loop just before midnight.
Officers responding to a call at a convenience store near 16th and Michigan spotted the suspect.
He fled and was caught in an alley near 18th and Wabash after a brief chase.
Police say he was carrying a Mac 11, which is like a mini-machine gun with a clip holding more than 30 bullets.
Cash from the robbery and a small amount of marijuana were also recovered.
The arrest was made less than a block from the 1st District police station.
Charges are pending.