70-year-old punched in face during robbery at CTA Blue Line station

CHICAGO -- Chicago police are looking for a man who pretended to be a police officer, then robbed and beat a 70-year-old on a CTA platform.

The 70-year-old man was standing on the Blue Line subway platform at Dearborn and Monroe just before 3 a.m. Tuesday.

Another man, who claimed to be an undercover police officer, approached him and asked to see the elderly man's identification cards.

The 70-year-old took out his wallet and the man grabbed it. The elderly man fought back and the attacker punched him in the face and ran away.

The victim was taken to Northwestern Memorial Hospital and is in stable condition.

Investigators will examine surveillance video to try to identify the robber.

No one is in custody at this time.