The man apologized, said he was looking for an electrical outlet, and left, the police said.
The incident, which was reported to students in an alert sent Wednesday night, comes on the heels of a rash of other reported sexual assaults.
According to the university, there have been eight sexual assaults - including the four in the last month - in 2014. That tops the number of sexual assaults reported in all of 2013, six, Sheridan said.
For the years 2010, 2011, and 2012, the campus reported five, six, and seven sexual assaults respectively, according to the campus's public safety office.
Sheridan said the spike could mean more women are reporting assaults, not that more are taking place. Sexual violence is the most underreported crime on college and university campuses, according to Alison Kiss, executive director of the Wayne-based Clery Center for Security on Campus.
Sheridan said the police do not believe the four most recent incidents are related.
In the first two - one March 30, the second April 4 - female students said they were sexually assaulted by men they knew. In the third, which the police said took place early Saturday, a female student said she was assaulted in a campus residence by a man she did not recognize. That man was described as being a white male, 5-foot-4, of small, thin build, wearing a black hoodie.
The police have described the man involved in Wednesday's alleged assault in the library as a white male about 50 to 60 years old with a receding hairline. Sheridan said a university police officer was in the library at the time, but the man left before the student reported what happened, about five minutes after the incident.
"The fact that there is video on him, that there were cameras, we do have some hope to be able to identify him," she said.
After the third assault was reported to students, several women outside the Sykes Student Union on Monday said they still felt safe on campus but were taking extra precautions, such as walking with friends at night.
"I make sure I'm not walking alone," sophomore Amirah Gee, 19, said. "If my friends are out, I say, 'Text me when you get to your room,' so I know they're OK."