A creep fired a gun at cops investigating the sexual assault of a woman in Brooklyn Sunday night, hours before another woman was raped on a rooftop in another section of the borough. In the first incident, a 21-year-old woman was sexually assaulted by a stranger on the street.

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The victim, who was taken to Coney Island Hospital, gave cops a description of the sicko.

When officers in a patrol car pulled up to a man walking on Neptune Ave. who matched the description, the suspect fired a gun at them and fled, police said.

Nobody was hit and cops did not return fire.

Police are offering a $12,000 reward for information leading to the arrest of Norman Vanigas, 23, who they believe is the shooter. Investigators are trying to determine if he also sexually assaulted the woman.

Vanigas is described as Hispanic, 5-foot-5, 140 pounds, with black hair and brown eyes.

Three hours later, in an apparently unrelated incident, a woman was snatched off the street and raped on a rooftop by a man with a box cutter.

The victim was waiting for a cab on Bergen St. in Crown Heights when her attacker dragged her to a rooftop about 2 a.m., officials said.

She was taken to Kings County Hospital.

Police are looking for her attacker, who is described as light-skinned, 5-foot-4 with a medium build and wearing a black baseball hat, white T-shirt and dark pants.