A citywide search is on for the man who shot a police officer Monday.

While Officer Robert Ralston was patrolling the 19th District near 56th Street and Lancaster Avenue, he stopped two men who’d been acting suspiciously near railroad tracks. One of the suspects ran away, but the other put a gun to Ralston’s head.

Ralston, 46, and with 21 years on the job, pushed the gun away, and was struck in the shoulder when the suspect fired. The father of five, who lives on Comly Road near Rambler Park, was treated for his wound at the hospital, but returned to the scene to assist with the investigation.

Police dogs were unable to trace the suspect, who ran east on the tracks. He remains at large, and has a mark or tattoo under his left eye.