After a series of pizza delivery robberies in Montgomery County, police began to focus on one suspect. They also asked pizza outlets to report orders that seemed suspicious. When a suspicious order came in Monday night, police said they were watching their teen-age suspect’s home and saw him leave through a bedroom window.

They said they watched their suspect walk toward Smoothstone Way in the Montgomery Village area, where the pizza was to be delivered. As he walked, the suspect put on a black mask, police said.

The suspect hid in bushes at the house where the suspicious order was to be delivered, police said. Officers then canceled the order. A smartphone app advised the suspect of the cancellation, police said.

A new order was soon sent in for another house on the same block, police said. That, too, was canceled by police, whereupon the suspect headed home.

Police said a short foot chase ended with the arrest of Marcus A. Addison, 17, of Mills Choice Road in the Montgomery Village area. They said they found a pellet gun, which had apparently been discarded during the chase.

Police said Addison was charged as an adult with two counts of attempted robbery in the incidents Monday night and with six counts of armed robbery in connection with earlier incidents in the Gaithersburg and Montgomery Village areas.