Both crimes in Gramercy were caught on camera, the latest on Wednesday.
The suspect followed a 71-year-old man into his building, threw him to the ground and stole some cash.
The victim broke his arm in the scuffle.
Police believe the same suspect also attacked a 77-year-old man on November 3rd.
The victim was roughed up and robbed, then the suspect ran away.
The suspect is described as a male, black, approximately 5'8" in height, 180 lbs. He was last seen wearing eye glasses, a light colored shirt, a baseball hat, blue jeans, and sneakers.
If you can identify him you're asked to call Crime Stoppers at 1-800-577-tips.