Nevada School Shooting 'Hero' Teacher Was Former Marine Two boys are in critical condition, while the shooter is believed to be dead.

Oct. 21, 2013 -- A middle school math teacher was shot dead today while shielding students from a boy with a gun in a Nevada middle school.

Two students were shot and wounded before the boy with the gun was killed. It's not clear how he died, but police said they did not fire any shots.

The slain teacher was identified by his family as Michael Landsberry, a former U.S. Marine.

"In my estimation is he's a hero," Reno's Deputy Police Chief Tom Robinson said at a news conference.

Chanda Landsberry, the slain teacher's sister-in-law, told ABC News that he left beind a wife, Sharon, and two step-daughters.

The two wounded boys were taken to Renown Regional Medical Center and were initially listed in critical condition, hospital spokeswoman Angela Rambo told ABCNews.com.

Authorities said one of the students has been through surgery, while the second is said to be "doing well."

It was the first day back from fall break when gunfire erupted around 7:16 a.m., a "time in the morning students are arriving, buses are arriving, the walkers are coming in through the gates outside. Kids are congregating out back….waiting for their day to start," Washoe County School District Chief of Police Mike Mieras said.

Witnesses said the suspect first opened fire on the basketball court, where he shot a boy in the arm.

"I heard the first shot," a student named Jonathan told the Reno Gazette-Journal. "I looked over and saw a kid, my best friend, laying on the ground shot in the arm."

At that point, students said Landsberry rushed in to try and stop the boy from shooting anyone else. The suspect told Landsberry to back up, and when he did, witnesses said he boy shot the math teacher in the chest.

While the shooter ran into a school building, where he hit another boy, Andrew Thompson, a student at the school, said he and his friends tried to save Landsberry.

"Me and five other friends said, 'Come on, we have to get him to safety,'" Thompson told ABC News' Reno affiliate KOLO-TV. "We picked him up, carried him a little bit far, and then left him because our vice principal came along and said, 'Go, go, go! Get to safety.' So we left the teacher there and went to safety."

Police said today they are hoping to interview the estimated 20 to 30 witnesses who heard or saw gunfire and hope by talking to students they will be able to determine the suspect's motive and whether he shot indiscriminately or was targeting specific victims.

"The best description is chaos," Robinson said.

The 630 students enrolled at the school were evacuated to nearby Sparks High School where they are waiting to be released to their parents, Washoe Schools spokeswoman Terry Bartek told ABCNews.com.

Administrators said school has been cancelled for the remainder of the week and grief counselors have been brought in to help students and staff cope with the ordeal.

Gov. Brian Sandoval said he was "deeply saddened to learn of the horrific shooting" and is receiving regular updates from authorities who are working at the scene.