CAMBRIDGE, Mass. - Four buildings on Harvard University's campus were evacuated Monday after police received an e-mail claiming that explosive devices may have been hidden inside, but after hours of searches and disruptions to final exams, no suspicious devices were found.

The buildings were evacuated and access to Harvard Yard was restricted after the e-mail was received about 8:40 a.m. Monday, shortly before students were to begin final exams.

Investigators from several agencies searched the buildings for hours and cleared students to return to all four by mid-afternoon. One of the buildings was a freshman dormitory; classes are held in the other three.

In a statement to the Harvard community, Harvard executive vice president Katie Lapp said the buildings were evacuated "out of an abundance of caution" and that activities were returning to normal.

"I am relieved to report that no suspicious devices were found," Lapp said.

She said Harvard police, and local, state and federal authorities, are continuing to investigate to find out who is responsible.

Harvard officials would not comment on speculation among students that the e-mail was a hoax timed to coincide with finals at the school.

Harvard did not say when students would be allowed to take the finals that were canceled because of the evacuations.

The mood was calm as students streamed out of Harvard Yard on a morning with temperatures in the 20s.