Two adults were wounded and were taken to Creighton University Medical Center. Their identities and conditions were not immediately known, and Bettin did not have any further details about the suspect and how he died.
A 16-year-old student at the school told The Associated Press she was just beginning lunch when the principal rushed into the cafeteria.
"He was like yelling, 'Get in the kitchen! Get in the kitchen!' He was waving his arms. You knew something was wrong and it wasn't a drill," said Laura Olson, who is the daughter of an AP reporter.
Olson, a junior, estimated that she'd been rushed into the kitchen with several dozen students around 12:45 p.m.
The school was on lockdown after the shooting, but by 3 p.m., students were being released in groups from the school. Parents were allowed to pick them up at a nearby church.
The high school sits on the west side of Omaha, within city limits, and has about 2,100 students.