The gunman, police now say, was a 12-year-old boy, a seventh grader, and the gun was a 9 millimeter semiautomatic Ruger handgun.
"We believe that the student got it from his residence," said Tom Miller, deputy chief, Sparks police.
911 calls show how the boy gunman terrorized the school yard outside Reno, Nevada, just minutes before the morning bell rang Monday.
"Somebody brought a gun to school that shot a teacher."
The memorial for Mr. Michael Landsberry continues to grow. The vet, who served twice in Afghanistan, turned math teacher, was killed as he tried to stop the shooting.
"Cannot express my appreciation for Mr. L," said Superintendent Pedro Martinez. "He truly is a hero."
Two other boys shot before the gunman killed himself. They are expected to survive. And now, police are looking into whether the boy shooter's parents might be criminally responsible.
"Did they knowingly permit their child to have access to this weapon? If there is enough circumstantial evidence... then it's entirely likely that they could charge the parents criminally," said Mark Geragos, lawyer.
There's still no known motive and no name. Police say they may never reveal the identity of the young killer, out of respect for his grieving parents.
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, Landsberry, 45, 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."
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 are cooperating with the investigation.
"Everybody wants to know why - that's the big question," 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.
"His actions yesterday I believe saved the lives of many children," added Col. Jeffrey Burkett, commander at the Nevada Air Guard's 152nd Airlift Wing where Landsberry served.
Police said they believe the shooter at one point tried to enter the school but couldn't open the door because of emergency lockdown procedures.
After killing Landsberry, the boy fired at a second student, hitting him in the abdomen. He then shot himself in the head.
The two 12-year-old boys who were wounded are in stable condition and recovering.
Parents clung to their children at an evacuation center shortly after the shooting while the community struggled to make sense of the latest episode of schoolyard violence, which happened less than a year after the Newtown, Conn., massacre.
Sparks, just east of Reno, has a population of roughly 90,000.
Under Nevada law, it is illegal to allow anyone under 18 to handle a gun without supervision. The offense rises to a felony if there was substantial risk the child would use the firearm to commit a violent act. However, the law doesn't apply if the gun was stored securely or if the child obtained the weapon unlawfully.
Landsberry was married, had two stepdaughters and coached several youth sports. He also served once in Kuwait and two tours in Afghanistan with the Nevada National Guard and was well-known in the school community. He served in the Marine Corps from 1986-90 and was stationed in Camp Lejeune, N.C., and Okinawa, Japan, according to military records.
His bravery came as no surprise to his fellow airmen.
"That's who he was," Chief Master Sgt. James Ross told reporters at the air base in Reno on Tuesday.
Senior Master Sgt. Robert Garrett attended middle school with Landsberry in Reno before serving as his supervisor in recent years. He described him as a tough ex-Marine who taught with compassion and was known as a Batman fan and soccer fanatic who would do anything to help anyone.
"Every one of the people I have talked to just knew that Mike was in there," Garrett said. "He was the guy that would have jumped in there to stop the bullets from hitting other kids. And sure enough, it was."
Mayor Geno Martini praised the response from officers, who arrived at the scene within 3 minutes of the initial 911 calls to find the shooter dead.
"You can never plan for anything like this," Martini said Tuesday.
Students from the middle school and neighboring elementary school were evacuated to a high school, and all classes were canceled. The middle school will remain closed for the week, while an adjacent elementary school is set to reopen Wednesday. A candlelight vigil was planned Wednesday night outside the middle school and a multi-faith prayer vigil at a church in neighboring Reno.
Ferro's dad took the day off and the two went out to lunch together on Tuesday, a day Ferro thought might never come.
"I'm still a little shaken up, depressed and confused," Ferro said. "The whole time I was hoping Mr. L. was OK, we'd all get through it, it was a bad dream."