Denver police are warning citizens to watch their backs.

A serial buttocks-groper is on the loose, and Crimestoppers is offering a reward of up to $2,000 to catch him.

Police think the same man who fondled a woman’s backside at East Fifth Avenue and High Street on Aug. 21 grabbed another woman’s buttocks a few minutes later a block away on East Fourth Avenue.

Tuesday night, another woman was grabbed on the buttocks at an alley entrance between Newton and Osceola streets along West 37th Avenue.

The groper is described as Hispanic, in his late 20s to early 30s, about 6 feet tall. He also is described as bald and heavy-set.

He was seen driving away in a black four-door Nissan Altima or Maxima with tinted windows and shiny rims.

Anyone with information can call Crime Stoppers at 720-913-7867.