Although the threats received more attention after a gunman fatally shot one person and wounded several others before he was shot dead by campus police at a University of Pittsburgh Medical Center psychiatric hospital on March 8, the string of threats actually began on Feb. 13.
At first, the threats were scrawled on bathroom stalls. Lately, they've been emailed - sometimes to reporters for the city's two major newspapers, the Pittsburgh Post-Gazette and Pittsburgh Tribune-Review.
Two new threats against sets of buildings were received Thursday, one at 10 a.m., the other about 12 hours later. Police and experts say the sender is using an online "remailer" that relays emails through several intermediaries so the origin of the message cannot be traced, though some emails apparently were routed through computers in Austria.
"It would be very difficult if not impossible to trace this," said Lorrie Cranor, who oversees Carnegie Mellon University's CyLab Usable Privacy and Security Lab a few blocks from the Pitt campus.
No bombs have been found and nobody has been injured, though some are beginning to question the futility of building evacuations and searches.
"All this is still worth it," campus police Chief Tim Delaney said earlier this week as bomb-sniffing dogs searched the 42-floor Cathedral of Learning, which has been targeted by at least eight of the threats. "I will never put kids in danger."
Andrew Sours, 21, a junior from the nearby suburb of Jefferson Hills, said one of his professors is holding class online as a result.
"Because it happened so many times, it spooked people, and they emailed the professor and said they're scared to come to class," Sours said.
Others like Hannah Bitzer have decided to commute from her home in Fox Chapel, another nearby suburb, instead of remaining in her dormitory, even though that particular building hasn't been threatened.
After an emailed threat against three buildings Wednesday night, Bitzer, a freshman, said, "That's when I called my mom and said, 'please come and pick me up because I no longer feel safe on campus.'"
The FBI has not returned calls from The Associated Press, but agents are working on tracing the emails and other threats and profiling whoever the person or persons are who sent them.
U.S. Attorney David Hickton in Pittsburgh issued a statement Friday commending Pitt's response and confirming the threats "are being vigorously, aggressively and thoroughly investigated through every possible mean" by the region's Joint Terrorism Task Force, which includes the campus police and FBI.
Retired FBI profiler Mary Ellen O'Toole of Stafford, Va., believes one person, likely a man, is responsible.
"Now he's doing this for more fun, power and excitement," said Stafford, who believes the first few threats might have been to get classes canceled or be rooted in some other problem.
"He's scaring the heck out of the students; he's causing a lot of pain, but he's not getting that. There's an emotional disconnect there," she said. "There's a lack of empathy."
