An alleged sex assault on the nineteenth floor of the W.E.B. DuBois Library has some UMass students on alert.

A day after an alleged sexual assault in the University's library, some of the 10,000 female students are on edge.

"It was weird to know that she was on the nineteenth floor and this happened," UMass sophomore Julia Seavey said.

With midterm exams on the minds of undergrads, it was a late night of studying on one of the top floors for one UMass student on Tuesday night.

Campus police said she went to the restroom, and there, a man in his 20s or 30s was lying in wait.

"It's scary to know that people are lurking in the place you go to study," UMass junior Sharnia Dottin said.

The campus is on the offensive. According to UMass Police, the campus saw 11 forcible sex offenses reported last year.

In the tall shadows of Tuesday's crime, university officials on Wednesday, were scoping out the areas that predators seek out.

"We try to find defects whether that may be lighting or other physical plant issues," said Patrick Archbald, deputy chief of UMass Police.

While that group seeks out safety hotspots, others stay in groups of their own, saying their sense of security is lost.

"A lot of my male friends will escort me places at night once its dark out on campus, and I'm like, 'don't worry about it. It's just a five minute walk,' but now I'm like, 'please, it's just a five minute walk,'" Seavey said.

The nineteenth floor is full of windowless study rooms with locked doors. No physical security presence is on that floor, and the University is now looking into safety measures.