CHICAGO (CBS) — A warning for CTA Green Line riders. Authorities want people to hide their phones.

Chicago police released images of a man who, on December 12, was suspected of approaching a rider on the Roosevelt stop platform and told the person he had a gun.

The suspect took off with the victim’s cellphone.

CPD said it is looking for a man who on December 1 allegedly flashed a gun and grabbed a rider’s phone while on the train near the Cermak stop.