Hero dad who took down school shooter speaks out: 'I was supposed to be there'

Tonight, we're hearing for the first time from the Oregon man who ended a deadly rampage at an elementary school in Bend, Oregon. Caleb Giamonco ran into Silver Rail Elementary on October 15th after seeing someone wearing black and carrying a long gun head into the school. Giamonco has two daughters who attend the school. He says he felt he was the children's last line of defense. He grabbed a handgun from his truck's center console, called 911, and went after the gunman. He said, I'm sorry, I have to go in. People are going to die. The 16-year-old shooter attacked a special education classroom, killing three children, ages 5, 8, and 11, and a teacher. Another student was critically injured, and a teacher was hospitalized. Giamonco said he laid on his stomach and used his elbows to crawl across the ground, eventually entering the school through a window that had been shot out. Inside, he confronted the shooter, who was struggling with an unarmed teacher. He was scrambling for his weapon, and I looked at him, and I shot him two more times to make sure that he couldn't move because I was afraid of him shooting anybody else. Giamonco says he feels he failed the families of those who died. I want to apologize for not saving their babies. That's probably the biggest thing for me right now. Police say Giamonco was legally carrying his gun. I can't tell you what it feels like to take a life, but I can tell you that I genuinely feel like I was supposed to be there. And if I wasn't there, I just don't know what would have happened. Police credit both Giamonco and the teacher who confronted the gunman with saving lives. Jacqueline Lee, ABC News, Los Angeles.