BOSTON -- Officials at the University of Massachusetts at Amherst are looking for a man who sexually assaulted a female student in a library bathroom on campus on Tuesday.

The attack happened between 10 and 11 p.m. Tuesday in a 19th-floor bathroom of the Dubois Library.

The area where the attack occurred is a narrow, windowless passageway that has rows of locked and unlocked doors to offices and study rooms.

Several students said it wasn't safe and the attack triggered a campus-wide alert and calls for more security from students.

"They should have more security there because there's really not security or anyone patrolling much. Every time I've ever been there doing homework there's no one on the floors," said one student.

"I'd like to know what this person looks like," said another.

The attacker was described as a white man in his 20s or early 30s, 5 feet 6 inches tall with brownish, dirty blonde hair who was wearing a gray sweatshirt and blue jeans.

UMass Amherst reported four forcible rapes last year, four fondlings and two sexual offenses on campus. There was one rape reported and eight fondlings in 2007.

Students said there is such an open-door policy at the library that they often find homeless people frequenting the building, usually on the fifth floor, sometimes sleeping there.

There are 26,000 students, and about half of them live on campus.

"I don't ever see security walking around except on weekend nights," one female student said.

"Even just like more cameras for security downstairs would be better, safer," said another.

A university spokesperson said UMass is in the midst of an aggressive investigation but they would not say whether the victim and attacker were students or whether they even knew each other.

Anyone with information regarding this incident is asked to call the UMPD Detective Bureau at 413-545-0893 or the TIPS line at 413-577-TIPS (8477) or via the Anonymous Witness Form.