Police ended their search for a possible second suspect early in the afternoon, saying authorities believed the gunman was a student at the university and that he had acted alone. No other injuries were reported.

The nearly 50,000-student campus — whose clocktower was the site of one of the nation’s deadliest shooting rampages four decades ago — had been on lockdown while officers with bomb-sniffing dogs carried out a building-by-building manhunt.

Campus police spokeswoman Rhonda Weldon said a man fired an automatic weapon on the sixth floor of the Perry-Castaneda Library, then shot himself dead. Austin Police Chief Art Acevedo said the weapon was an AK-47.

Acevedo said police were investigating what he described as a second crime scene outside the library where shots also were fired.

Campus police Chief Robert Dahlstrom said officials later ruled out the possibility of a second shooter, explaining the initial confusion came about because the gunman had fired shots in multiple locations. He said the suspect wore dark clothes and a ski mask.

Randall Wilhite, an adjunct law professor at the university, said he was driving to class when he saw “students start scrambling behind wastebaskets, trees and monuments,” and then a young man carrying an assault rifle sprinting along the street.

“He was running right in front of me … and he shot what I thought were three more shots … not at me. In my direction, but not at me, clearly not at me,” Wilhite said.

The professor said the gunman had the opportunity to shoot several students and Wilhite, but he did not.

The university canceled classes for the day as law enforcement officers patrolled the campus with dogs searching for suspects and explosives. Police and university officials locked down the campus for several hours and early afternoon issued an all clear.

The university posted a notice on its emergency information website emphasizing that the school remained closed and that the area around the Perry-Castenada Library was still an active crime scene.

Jennifer Scalora works in admissions about 100 yards from the library. She said the campus — one of the biggest in the country — was quiet and empty except for police, SWAT teams and helicopters.

“The students did their part, they cleared the streets, they cleared the grounds in a very quick manner,” Acevedo said.

Tuesday’s shooting was not the first at the school.

On Aug. 1, 1966, Charles Whitman went to the 28th floor observation deck at the UT clock tower in the middle of campus and began shooting at people below. He killed 16 people and wounded nearly three dozen before police killed him about 90 minutes after the siege began.

The Perry-Castaneda Library is one of several on the campus and is one of the busiest undergraduate libraries.

Student Joshua Barajas, 23, said he usually is in the library in the mornings but was delayed Tuesday when he made a rare pit stop for coffee.

“These little mundane decisions could save your life. If I hadn’t stopped for coffee — and I never stop for coffee because it’s $4 — I could have been in that building,” Barajas said. “It’s creepy. I don’t even want to think about it.”

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Associated Press writers April Castro and Jim Vertuno in Austin, Ramit Plushnick-Masti in Houston and Diana Heidgerd in Dallas contributed to this report.