College of Charleston President Glenn McConnell called the alert system mistakes made in Tuesday’s bomb threat “unacceptable” and said he will immediately work to correct them.

Five days after police swarmed onto the University of South Carolina campus after a double shooting in a classroom, officers with rifles burst into some classrooms at the college to deal with then threat.

Concern escalated when students and staff received a Cougar Alert saying a bomb had been found.

No bomb was found, but hundreds of students milled about while police searched buildings and grounds in the heart of the campus.

Police received a 911 call about 10:40 a.m. that bombs were in the Beatty Center and in Craig Hall, police spokesman Charles Francis said. He said police showed up with military-style rifles because they didn’t know what to expect.

“It came in as a bomb threat, but you don’t know how the situation might change, so you have to be prepared in case the situation changes,” he said.

The confusion was made worse after the school sent out a Cougar Alert saying a bomb had been found on campus. A new Cougar Alert went out a few minutes later, saying there was no bomb, only a bomb threat, and students and staff should follow police orders and remain alert.

College spokesman Mike Robertson said a dispatcher at the school misunderstood the message from the police department, resulting in the mistaken alert.

“In either event, we wanted people to evacuate the area, and that was accomplished,” he said.

McConnell, who was in his office at the time the bomb threat was reported, released a statement in the afternoon saying he appreciates everyone’s patience and the efforts of public safety to clear the area. But the events of the day left a concern about alert mistakes, he said.

“Our emergency notification system — Cougar Alert — proved less than effective in a real-time situation. In the aftermath of today’s events, we have learned that there was a glitch in the system, programmed years ago — which resulted in our communication protocols being compromised, and the initial ‘bomb found’ message was sent out electronically in error,” he wrote. “Also, the mechanisms for communicating quickly through the Cougar Alert system — by phone, text and email — did not reach all constituents. Plain and simple, that is unacceptable, and I will work with our emergency management task force to address it immediately.

“Our first and foremost priority at this institution is for our students’ and College community’s safety. While we may hope something like today is never repeated, we must be better prepared in dealing with it. And I assure you that we will.”

After the bomb threat was received, police blocked off George, St. Philip and Liberty streets, and part of King Street, set up a command center and started searching buildings. Officers with rifles were also seen searching the grounds.

Classes in the areas that were blocked off were canceled for the afternoon. Craig Hall, Liberty Street Residence Hall, the J.C. Long Building, Beatty Center and Tate Center were evacuated.

Restaurants and other businesses on George and Liberty streets were also closed because of the threat. A customer trying to get into Caviar & Bananas on George Street was turned away by an officer.

Andrew Aikman, a sophomore from the Isle of Palms, said he was shocked to see police with guns on campus.

“I was actually quite frightened,” he said. “It seemed like the police were taking over. I figured it was either a school shooting or a bomb threat.”

He left his wallet and books in his room, so he couldn’t study and had no money while he waited for the all-clear.

Around 12:30 p.m., officers extended the barrier farther down St. Philip Street to the Simons Center for the Arts, and a Charleston Fire Department hazmat vehicle backed up the street to take up a position.

Police cleared the scene by 4:30 p.m. and announced they didn’t find a bomb and no suspects were identified. Classes were set to resume at 5 p.m.

Agencies called in to assist the college and its public safety officers include the FBI; Charleston police and fire; Ports Authority police and the Air Force Base bomb squad.

Melissa Boughton contributed to this report. Reach Dave Munday at 937-5553.