A woman told officers a man came to her apartment around 10 a.m. and said he was there to do a repair.
The man came into the apartment and pulled out a handgun, but the woman was able to get away and was not injured.
Police did not elaborate on why the incident was sexual in nature.
"I just hope that something is done about this because this is Duke," said Nia Bostick, a Durham resident. "it's very scary because there are a lot of college students in this area and nothing like that has ever happened before."
Lizzy Blake said she saw officers outside her apartment when she went to work this morning.
"I thought it was weird because there weren't any extra unusual cars here," Blake said. "Yeah, it's worrisome that someone approached you and you thought it was the maintenance man.
"I've seen our maintenance guy so but also maybe we got someone new," she added. "I personally wouldn't let anyone in my apartment unless they had a shirt or whatever."
The suspect is described as a black man, 35 to 40 years old, 5 feet 9 inches to 6 feet 2 inches tall with a heavy build. He had a slight beard, a thin mustache and close-cut hair.
He was wearing a dark blue T-shirt with lettering, black knee-length shorts, and black sneakers. He had a gray handgun.
Zak Kramer, a Duke grad, said the incident gives him pause.
"It just makes you think about who, when you make a maintenance call, what you're going to worry about and who has access to your apartment when you're not there," Kramer said. ""I watch out. I'm not on my phone all the time. I'm looking around just make sure you're alert."
Anyone with information is asked to call Inv. Bynum at (919) 560-4440, ext. 29238 or CrimeStoppers at (919) 683-1200.