The school received the threat against multiple buildings around 9 a.m. and decided to evacuate just before 10:30 a.m., Princeton spokesman Martin Mbugua said, noting that officials at the New Jersey Ivy League university took that time to assess the threat.
Sources told Action News that the person who called in the bomb threat was a "known caller," and the threat was credible.
Nearly 7,000 students, faculty and university workers were evacuated from the campus and off-campus buildings. Faculty and staff were sent home, while students were told to go to nearby public places.
The evacuation order then remained in place for nearly eight hours as the university's Public Safety department worked with multiple law enforcement agencies to sweep numerous campus buildings with bomb-sniffing dogs.
Later, Princeton issued a statement saying the bomb threat was one of a number of threats around the country Tuesday. But a university spokesman said he was unaware of anything linking them.
No classes were in session Tuesday, though some summer programs were.
Brandon Blau, 20, a chemistry major from Long Island, N.Y., was in a lab working on research when the threat was announced. By the afternoon, he and fellow chemistry students were hanging out on a street near campus, checking a laptop for updates on when they could return.
"You want to be safe about it, but we also want to get back on campus," Blau said. He and his friends are doing research this summer.
Fellow chemistry major Hudson Beard, 21, of Abilene, Texas, said the reported threat was unusual enough that they realized it needed to be taken seriously. He joked that the threat had at least brought some excitement to the campus while most students are on summer vacation.
The Associated Press contributed to this report.
