A man who robbed the Citizen's Bank at 17th and Market Streets this afternoon was arrested after being trapped between interlocking doors, a security system known as a man-trap, police said.

The suspect, who has not been identified by police, fired his gun in an unsuccessful attempt to free himself. He was taken into custody.

The man walked into the bank just before 3 p.m. and produced a gun and a note demanding cash. The teller handed over an undisclosed amount, police said.

On his way out, he was snared between the doors. The man-trap system could have been tripped by a bank employee, police said.

Contact staff writer Troy Graham at 215-854-2730 or tgraham@phillynews.com.