ATLANTA — A student disguised with a ski mask and armed with an AK-47 assault rifle terrorized the University of Texas, Austin campus Tuesday morning, firing five shots before killing himself on the sixth floor of the main library, authorities said.

Police initially searched for a second suspect because witnesses gave differing descriptions of the man. But after searching the campus for a few hours, officials declared that the student had acted alone.

“”We did get multiple descriptions, and we have to make sure that he didn’t have other people with him,”” University of Texas Police Chief Robert E. Dahlstrom said. “”We do not feel like there were, but we have to check out every lead.””

The alleged shooter, who was found on the sixth floor of the main Perry-Castaneda Library with apparent self-inflicted gunshot wounds, had not been identified Tuesday afternoon but was a UT student, said Robin Gerrow, the school’s assistant vice president of public affairs.

No other injuries were reported, but the event shook the sprawling campus, which was the site of one of the most notorious American school shootings. In 1966, troubled student Charles Whitman shot and killed 14 people and injured more than 30 from the observation deck of UT’s iconic tower.

A number of witnesses reported seeing the gunman armed and on campus around 8 a.m. Law professor Randall Wilhite told CNN he was in his car and on his way to teach a morning class when he heard gunshots, then saw a man in a dark suit, tie and ski mask running with an assault rifle and firing shots.

“”When I pulled up in my car he was sort of right in front of me and didn’t stop running, but turned in my direction and fired, like, three shots into the ground to the left of my car,”” Wilhite said.

He saw students scatter, running away and hiding behind trees. But, Wilhite said, the masked man did not pursue them. “”It appeared to me he was not inclined to shoot anyone,”” he said.

Freshman Andrew McWaters was walking on campus toward his dorm room when he heard gunshots. At first he thought it was a student demonstration. But then he heard a second round and ducked into a nearby auditorium. McWaters said he saw the shooter, in a black ski mask, wave and smile through the mouth of the mask.

Wilhite said the man was running toward the center of campus and the library.

The campus was locked down for a number of hours and classes were canceled for the day. Dahlstrom said that no motive had been established.