(CBS) –Spiderman is a hero in the movies, but he’s turning out to be a bad guy in Chicago.

Chicago police detectives on Friday were studying surveillance tape from a robbery the night before. An armed robber wearing a Spiderman mask hit a convenience store in the 3700 block of North Harlem Avenue.

There were extra cameras at a 7-11 in the 2700 block of Harlem because the same masked man hit the store last month and again on Tuesday.

An employee told CBS 2’s Dorothy Tucker: “It’s a little nerve wrecking because he might strike again. Maybe it might happen on my shift.”

This latest string of robberies comes on the heels of similar attacks on small business by the so-called Subway bandit. That robber hit 16 stores, mostly Subways, before police arrested him Tuesday night.

“Guys get in their head to start doing a certain type of robbery. They start feeling comfortable with the type of robbery they’re doing and the way they’re doing it. They just get in a groove and they just keep going until we get them,” Chicago Police Sgt. Andrew Schoeff said.

Chicago police say the “Spiderman Bandit” may have also struck in Elmwood Park.

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