His look was menacing, and those who encountered him fled fast.
"I saw in his eyes he didn't care," said construction worker Ruben Cordoba, who was installing a fence on the roof of a three-story building Tuesday morning when he looked down and made eye contact.
Authorities say the gunman whowas 19-year-old Colton Tooley, a sophomore math major. No one else was injured.
But those who knew Tooley for years - before his time at the massive university in Austin - describe him as a courteous, intelligent guy who wouldn't hurt anyone. He was book smart and won raves from his high school teachers. He also was known as someone who kept his emotions in check.
"There was nothing prior to this day, nothing that would lead any of us to believe this could take place," said a man who emerged from Tooley's family home late Tuesday and identified himself only as Marcus, a relative. He read a statement saying that Tooley's parents were distraught. "They've lost their child."
As the gunman trekked along a campus street with an AK-47, he fired three shots toward a church, then fired three more times in the air, Cordoba said. Police said that with help from students they were able to track the shooter's movements and chase him off the street. He went into the Perry-Castaneda Library, where he shot himself to death, said campus police Chief Robert Dahlstrom said.
Dahlstrom said it wasn't clear that the gunman was shooting at anyone in particular outside the library. The shots may have been fired into the air or missed shots, if he was aiming at someone, the chief said.
University of Texas president Bill Powers canceled classes Tuesday and said normal campus operations would resume Wednesday.
Police declined to speculate on a motive.
Marcus, the relative who said the family wasn't planning to make any further comments, said he wanted the public to understand Tooley.
"He was a very smart guy, very intelligent, excellent student. He wouldn't or couldn't hurt a fly. If he was depressed you would never know it. He never usually expressed emotion. This is a great shock to me and my family," he said.
Tooley's parents did not immediately respond to messages left by The Associated Press. Investigators combed through the family's home in Austin on Tuesday, carrying out bags and boxes. There was no word on exactly what was in the containers. A neighbor said police arrived about three hours after the shooting.
The gunman's threatening demeanor on campus was far from what Tooley's teachers at Crockett High School in Austin recalled of the boy who graduated in 2009, ranked seventh in his class. They remembered him as "brilliant," "meticulous" and "respectful," the principal, Craig Shapiro, said a statement.
"All of us in the Crockett High School community are shocked and saddened by today's tragedy at the University of Texas," Shapiro said. "Our hearts go out to the family and friends of Colton Tooley."
At the University of Texas, Tooley was a math major with an interest in actuarial science.
The armed walk went through the heart of the UT-Austin campus, where one of the nation's worst mass shootings took place from atop the clock tower in 1966, when Charles Whitman shot and killed 16 people and wounded nearly three dozen.
On Tuesday, seeing an assault rifle and hearing gunfire near a fountain in front of the tower caused a garbage truck driver to leap out of his vehicle and run away. A woman carrying two babies did the same.
Oscar Trevino, whose daughter Martina Trevino works in a campus dormitory, said she was walking to work near the library when she heard two shots behind her. She started to run and fell down, then heard another shot.
"She said she turned around and saw," he said. "She took off running."
University officials sent word through text messages and a campus website telling students, faculty and staff to stay put in buildings as the campus went on lockdown. Sirens and announcements blared on campus loudspeakers warning that there was an emergency.
Libby Gertken, an assistant French instructor, was giving an exam in a nearby classroom when she got an e-mail from the university notifying her of the gunman.
"We all got on the floor," she said. "We stayed on the floor for a while. A couple of brave male students got behind the door to stand guard."
She said the class came up with a plan to "all run at the person" if the gunman came into the classroom.
Nathan Van Oort, a junior from Boerne who was taking a chemistry quiz when the shooting started, said students in his class near the library got text messages and told the instructor what was going on. The teacher told students to keep taking the quiz, he said. Some, including Van Oort, stopped taking the test and ran out.
"She just thought it was a rumor," he said. "I couldn't believe it that she would blow it off."
Police ruled out a report of a possible second gunman, and about four hours after the gunfire, campus officials gave the all clear. The library remained cordoned off as a crime scene.
Dahlstrom and Austin police Chief Art Acevedo said the two departments and other law enforcement agencies had trained for such a scenario. It paid off, Dahlstrom said, and "probably prevented a much more tragic situation."
(Left: Smoke rises from Charles J. Whitman's gun as he fired from the tower of the University of Texas administration building on crowds below in this Aug. 1, 1966, file photo.)
In online forums and on Facebook, there was much praise for the university's emergency texting system, and in the emergency response, in helping make the evacuation quick and efficient.
"Thanks so much for everything, UTPD. Yall are awesome. I was locked in the UTC and felt completely safe the entire time. God bless yall," wrote Katey Psencik on the university police department's Facebook page.
On the UT website's emergency alert page, a commenter named Michelle wrote, "How ironic, the day we were to have a lecture defending 2nd amendment rights, we have a shooter instead."