A man who claimed to work at a cable company has sexually assaulted a 15-year-old girl in Woodbridge, police said.

The teen told police that she was in her home in the 4000 block of Echo Court in Woodbridge when she heard someone knocking at her front door. When she answered, a man asked to speak with someone who didn't live at the residence. The girl told the man that no one by that name lived there, and he left, Prince William County police said.

A short time later, the man returned and threatened the girl so that she would let him in. Once he was inside the home, he displayed what appeared to be a knife, forced the girl into a bedroom and inappropriately touched her, Officer Jonathan Perok said. The teen screamed and kicked toward the man, and he fled.

Police have released a computerized sketch of the man. He is described as black and in his 20s. He had a medium build and was last seen wearing a gray jacket, red shirt, black pants and black dress shoes.

Anyone with information can call Crime Solvers at 703-670-3700 or 866-411-TIPS.