And we begin inside that middle school in new mexico at the moment of crisis. When police say a 12-year-old boy with a shotgun walked in and started firing. And we are learning more, tonight, about a... See More
And we begin inside that middle school in new mexico at the moment of crisis. When police say a 12-year-old boy with a shotgun walked in and started firing. And we are learning more, tonight, about a possible warning message from the shooter. Abc's ryan owens leads us off with that and the 911 calls at the moment it happened. Oh, my god. Reporter: Tonight, we hear the voices of terror inside that middle school. 911? Hey. Berrendo middle school. A kid just got shot. Reporter: As investigators release those 911 tapes, they are also revealing for the first time, they believe the 12-year-old gunman premeditated this attack. And warned some students to stay away. We did find evidence that the suspect had planned this event. Reporter: They say he used his parents' shotgun and smuggled it on to campus in a duffel bag. In a gymnasium on tuesday morning, he shot an 11-year-old boy in the face, and 13-year-old sanders in the shoulder. Gabriel and his sister, brittany, were there. Gabriel was sitting behind the boy who was shot. It was frightening because you saw the blood. Reporter: Police believe there would have been more bloodshed if this eighth grade social studies teacher, john masterson, didn't put himself in the line of fire and talked the man into giving the gun up. He may not be the only hero teacher that day. Listen to another who called 911, as she comforts the guy who was shot. Talk to me, baby. I can't let you go into shock. You have to talk to me, okay? Reporter: If it feels like the mass shootings at schools or malls are happening at an alarming frequency, that's because the fbi says they are. Between 2000 and 2008, there were an average of five a year. Since 2009, the numbers have more than tripled. 16 a year. The children that return to school tomorrow were not the children who arrived on tuesday. Reporter: So, classes resume here in the morning. But plenty of questions remain. Among them, did the young gunman really try to warn some students to stay away from this gym? Or did, as police now think, he simply yelled something to some of them as he was running inside with a gun? Too late to do much good. Diane? All right, ryan. And we have a statement just in tonight from the 12-year-old alleged shooter's family. Saying, quote, on behalf of our entire family, we want to say, first, our constant thoughts, our fervent prayers are for those who are wounded. We are praying for them to recover. And for the medical personnel who are attending to them.
This transcript has been automatically generated and may not be 100% accurate.