More than 50 bomb threats disrupt University of Pittsburgh Gene J. Puskar / AP Students wait after being evacuated from class at the University of Pittsburgh following a bomb threat Monday morning.The threat was one of more than 50 since mid-February. More than 50 bomb threats since mid-February at the University of Pittsburgh have rocked the campus, sending professors to teach outdoors or online, WXPI.com reported. On Monday, as Pitt received yet more bomb threats, university security ratcheted it up its efforts, barring backpacks and packages from buildings. The Pittsburgh Post-Gazette reported that as a result, students waited in long lines outside certain buildings to reach their class. The threats began on Feb. 13, scrawled in felt pen on a bathroom stall, according to the Associated Press. Then the threats were e-mailed through a system that makes it nearly impossible to trace the message. Some e-mails were apparently routed through computers in Austria. No bombs have been found but nerves have been frayed. Tension was already high after a gunman killed two people and wounded seven before being killed by police in March. But the bomb threats continued after the gunman's death. Some, frustrated that they must make up classwork because of the evacuations, have questioned the futility of searching for so far nonexistent bombs. "All this is still worth it," Tim Delaney, the campus police chief, told the AP as bomb-sniffing dogs were dispatched to the Cathedral of Learning, a 42-story building. I will never put kids in danger. WPXI: Police stumped students irritated by Pitt threats Chancellor Mark Nordenberg addressed the suggestion that that the campus be shut down: "That alternative also had been considered but has not been viewed as the most appropriate choice," he wrote on the university's website. The university is offering a $50,000 reward for information that leads to an arrest. Retired FBI profiler Mary Ellen O'Toole told the AP she believes that one person, likely a man, is responsible. "Now he's doing this for more fun, power and excitement," O'Toole said. She said she 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.