District police are looking for a man who approached a woman on the pretense of helping her flag down a taxi in downtown Washington and then sexually assaulted her.

Police said the attack began Saturday between midnight and 1 a.m. at 19th and I streets NW, two blocks from the Farragut West metro station.

The woman told police she was trying to hail a taxi when a man walked up to her and offered to help. “The suspect led the victim to an unpopulated area near 19th and I streets, NW, where the suspect sexually assaulted the victim,” police said in a statement.

Police described the person they are looking for as a black male 25 to 30 years old, standing about 5 feet 8 inches tall and weighing 160 pounds. He has short hair, was clean-shaven and was wearing a red sweater with a hood and white shoes.