Authorities released 911 calls from students in the deadly school shooting in Sparks, Nev., on Monday where a 12-year-old boy allegedly killed a hero teacher, wounded two boys and took his own life.
"Somebody brought a gun to school. They shot a teacher," a male student, who sounded out of breath, said. He said the teacher was down and while he was on the phone, another gun shot was fired. "They, they, shot again."
It is unclear what prompted the boy -- who police are not identifying out of respect for his family -- to take a 9mm handgun from his home and open fire at school. Police said they've interviewed 20 or 30 witnesses and are looking into any prior connection the victims had with the shooter. The boy's parents, who could face charges in the case, are cooperating with the investigation.
Angelo Ferro, 13, was at the Sparks Middle School playground with friends Monday when he heard a pop about 15 minutes before the morning bell rang. He said he didn't think much of it -- it could've been someone popping a plastic bag.
But then he saw an injured boy clutching his wounded arm. He watched his fifth-period math teacher, Michael Landsberry, walk toward a student and fall to the ground.
"When he pulled a gun, we knew what happened," Ferro told The Associated Press on Tuesday.
Moments later, the eighth grader was cowered against a wall with some classmates, burying his face in his hands as a 12-year-old boy waved a semi-automatic handgun and threatened to shoot.
Ferro didn't know the boy, but said he and others in the frightened heap tried to talk him out of firing.
"You could hear the panic," Ferro said. "He left, thank God."
By the time police arrived, the 12-year-old gunman had killed Landsberry, wounded two boys and taken his own life.
"Everybody wants to know why -- that's the big question," Sparks Deputy Police Chief Tom Miller said. "The answer is, we don't know right now."
At a news conference Tuesday, law enforcement and school officials again lauded the teacher's actions, which police say gave students time to run for safety.
"I cannot express enough appreciation for Mr. Landsberry," Washoe County School District Superintendent Pedro Martinez said about the 45-year-old ex-Marine. "He truly is a hero."
The Associated Press contributed to this report