CHICAGO (CBS) — An off-duty Chicago police officer arrested a man who robbed a Loop bank where he was working as a private security guard on Wednesday.

FBI Chicago spokesman Garrett Croon said a man in his 30s wearing a black leather jacket robbed the U.S. Bank branch at 25 E. Washington St. at about 9:20 a.m.

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Witnesses said, as the robber was leaving the bank, an off-duty Chicago police officer apprehended him. The FBI said the off-duty officer works private security for the bank.

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“A guy walked in with a Dunkin’ Donuts bag, demanded cash, and on his way out the police undercover grabbed him, put him down, in literally like 15 seconds. It was amazing work,” Will Barton said.

Another customer called 911, and uniformed officers arrived within 30 seconds to take the suspect into custody.

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Chicago police arrest a bank robber who held up a U.S. Bank branch in the Loop on April 19, 2017. (Photo supplied to CBS)