Police are investigating a rape that happened early Wednesday after an unknown man invaded a woman’s residence in the southwest part of the city.

It happened about 3 a.m. Police would not give an exact location of the crime, saying that to do so might hurt the investigation. But they said the suspect and victim — a Lawrence woman in her 20s — did not know each other.

Sgt. Dan Ward, a Lawrence Police spokesman, said police were busy Wednesday examining the crime scene, conducting interviews and trying to find leads. The suspect is described as a white male in his 20s, about 6 feet tall with a slim build.

Because of the ongoing investigation, Ward would not release further details of the incident, such as whether the man entered the home by force.

He urged people to keep their window shades closed at night and lock their doors.

“I think if the police are reminding people of that, they’re doing it with good reason,” said Sarah Jane Russell, executive director of GaDuGi SafeCenter, an agency that provides services to victims of sex crimes.

Ward said the rape wasn’t similar to any other recent cases in Lawrence.