Police are searching for the man who sexually assaulted a woman in her Prospect-Lefferts Gardens apartment building, and they're hoping a sketch of the suspect leads to an arrest.

Police say the attacked happened Friday morning in the laundry room of the woman's building on Lincoln Road and Flatbush Avenue.

According to police, the 30-year-old woman was approached by the suspect, who exposed himself and demanded that she engage in sexual activity. When she refused, police say he threatened her with a knife.

The victim ran and found a neighbor, who called 911.

The suspect is described as 6 feet, 4 inches tall. He's in his mid-20s with a muscular build.

Anyone with information is urged to call Crime Stoppers at 1-800-577-TIPS.