AMHERST, Mass. -- Police said a woman was sexually assaulted inside the main library at the University of Massachusetts at Amherst on Tuesday.

The attack occurred on the 19th floor of the W.E.B. Dubois Library. The floor is full of windowless study rooms with locked doors and no security presence.

Investigators said the suspect attacked the student inside a restroom. The man is said to be a white male in his 20s or early 30s with brownish, blonde hair. He was last seen wearing a gray sweatshirt and jeans.

An alert has been issued by campus police and security has been enhanced in and around the library.

Students familiar with the building believe that the attacker knew where and when to strike.

"It has small hallways with nothing on the doors, no posters, it's not like this is a popular area. The person was obviously familar enough to come up to this floor where they know it's probably quiet," said student Kelly Rand.

“We'll probably have some discussion about the library and the cameras there and maybe if we could be doing more to make it safer there," said Deputy Chief Patrick T. Archbald of the UMass Amherst Police Department.

Anyone with information is asked to call police.

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