The University of Texas at Austin gave people the OK to leave campus Tuesday morning after a suspected gunman wielding an AK-47 fired shots and then turned the gun on himself inside a campus library.

The gunman died, said Robert Dahlstrom, chief of staff in the Austin Police Department. No one else was injured.

Police were checking campus buildings for possible explosives left behind, said Austin Police Chief Art Acevedo.

Authorities said earlier they were searching for a possible second suspect, but Dahlstrom said they now do not believe there is one.

Rhonda Weldon, a spokeswoman for the university, said authorities are tightening the perimeter for their investigation, and it will be around the Perry-Castaneda Library. This was part of an all-clear message from the university alert system.

The campus had been on lockdown, but Weldon said students were now allowed to leave, and shuttle buses were to transport students and staff away from the campus. The university canceled all classes for the day.

An ambulance was seen just before 9 a.m. in front of the Perry-Castaneda library, CNN affiliate KXAN reported. SWAT teams, armored vehicles and helicopters surrounded the campus.

The identity of the suspect and his motive were not immediately known.

“A suspected shooter in PCL library is dead,” said an alert posted on the university’s  emergency website at 10:30 a.m. “If you are off campus, STAY AWAY. If you are on campus, lock doors, do not leave your building. All organized classes for today, September 28, are canceled.”

Later the all-clear message was issued.

University of Texas professor Randall Wilhite heard gunshots on his way to class and saw students scrambling to safety. He said he saw a man in a dark suit and a ski mask pulled over his face running toward the direction of the library a little after 8 a.m.

Wilhite said the man was carrying what appeared to be an assault rifle and fired it randomly.

“When I pulled up in my car, he stood right in front of me and didn’t stop running but turned in my direction, fired three shots into the ground to the left of my car and kept running. I wasn’t sure it was real until I saw the bullets strike the ground to my left.”

Student Micah Geisenberg was already on a bus to the university when he received an e-mail alert to stay away.

“It’s chaos right now,” said Geisenberg, who heard a gunshot as he got off the bus near the library.

Matt Holiner heard a series of loud bangs from his dorm room, a couple of blocks south of the library. He suspected they might be gunshots, especially when he saw people running away. By mid-morning, there were at least 10 police cars outside his window.

“It’s been quite an exciting morning to say the least,” he said.