UPDATE 2:  All-Clear Given At University of South Florida In Tampa

TAMPA - Police have given the all-clear at the University of South Florida’s Tampa campus, more than two hours after reports of a gunman sparked a lockdown and massive search.

Two unidentified men were detained, although one since has been released.

The Tampa police bomb squad detonated a backpack left on a campus bus by the first man detained.

Officers yelled, “Fire in the hole, fire in the hole, fire in the hole” and then the backpack exploded. Its contents aren’t immediately known.

The series of events unfolded this afternoon with an initial report that a gunman was in the area of the USF library.

“Armed intruder on campus at the library,“ an alert on USF’s Web site stated. “Officers are on scene searching the area. Avoid the area and report anything suspicious.“

In an off-campus call transferred to USF police from the Hillsborough County Sheriff’s Office, a person reported that a man with a gun was in front of the university’s library, USF police Lt. Meg Ross said.

Campus officers were on scene by about 1:43 p.m.

Ross said she didn’t have any information about who placed the call.

At 2:30 p.m., three campus police cruisers that were parked at the library sped west, lights and sirens on, with one tearing across the library lawn and a curb.

About 20 minutes later, a man was handcuffed and placed in a cruiser in the area of Parking and Transportation Services. He was taken to the campus police station.

The man had stood up on a campus bus and said he was the person investigators were looking for and that he had a bomb, Tampa police spokeswoman Laura McElroy said. He later said it was a hoax.

After the man was detained, campus police quickly sent another alert to students saying another man, a white male carrying a black puppy and a large hunting knife, was seen in the area of Cooper Hall. The man was described as wearing a black tank top and a cowboy hat.

About 3:30 p.m., a man in a black tank top stood handcuffed beside a police cruiser near Cooper Hall.

That man has since been released.

USF junior Dylan Hodill was studying on the library’s fifth floor this afternoon when he heard sirens, looked out and saw campus police cruisers pulling up.

“I just got up and left my books and booked,“ said Hodill, 21. “I saw four cops come in with their guns drawn.“

Sean Byrne, 19, saw police searching garbage bins outside the library. He saw one officer holster his handgun and summon the other officers.

“They jumped in the cars,“ the sophomore said.

Luke Wortham, 28, was on the fourth floor of the library when he heard the first alert, the low-pitched sound of campus sirens.

Wortham, a sophomore studying pre-med, then heard people running up the stairs and yelling, “Put it down! Put it down!“

Soon after, he heard the sound of people running from the fifth floor.

Then things went quiet. A few minutes later, a police officer entered and told people on the fourth floor to leave.

The first man detained was on a campus shuttle bus at the transportation center. After he was taken into custody, students on the bus were led away.

The suspect was held in the back of a cruiser until he was driven away about 3:15 p.m., just as a bomb unit arrived from the Tampa Police Department.

Anahita Hassanzadeh, 25, was on a shuttle nearby, waiting to head to the engineering building when the driver told his passengers that a campus alert had sounded.

“We were in the shuttle and they told us to lie on the floor,“ Hassanzadeh said.

The students remained on the floor for about 10 minutes before they were allowed to leave.

Although police issued an all-clear at 4:20 p.m., they advised students and others to avoid police activity on Holly Drive near parking services.

In a statement posted on the college’s Web site and sent via e-mail this afternoon, USF President Judy Genshaft said the actions of police, students, staff and faculty “were prompt and effective.“

“We have a responsibility and an obligation to ensure everyone on campus is as safe as possible. … Please remain vigilant for any threat to campus,“ she said.