Investigators are trying to determine why a man wearing a ski mask opened fire with an automatic weapon on the University of Texas campus in Austin.
It happened on the sixth floor of the school's busy library.
Helicopters and armed vehicles quickly surrounded the scene.
SWAT teams moved in and text messages and e-mails were sent to students warning them of the armed suspect as administrators ordered a campus lockdown.
Police later found the gunman with a fatal self-inflicted gunshot wound.
"The suspect did commit suicide in the library building earlier this morning," Austin Police Chief Art Acevedo said. "No shots were fired by any law enforcement and we have not identified or found any injured."
In the confusion there were concerns about another possible suspect.
After they ruled out that theory, authorities gave the all clear, allowing students to leave campus.
U-T Austin has known tragedy from a school shootings, the most haunting in 1966 when a former student perched on the observation deck of the campus clock tower and opened fire on people below.
16 were killed before a police officer fatally shot the gunman.
Classes for the rest of the day were canceled, but police say campus should be completely open tomorrow.