Kirk Moore, the Oklahoma principal who tackled a gunman inside Pauls Valley High School last month, says "I don't know what I was thinking." 

"I just knew, I was just running to get to whatever was going on," he tells CBS News in a network exclusive interview airing Monday on "CBS Mornings."

Officials say his heroism ensured no one else at the school was injured and the suspect was arrested.

"I think it was just instinct," Moore says of his actions. "You know, in 37 years, you go through trainings and drills and what you should do. That all goes out the window."

Surveillance video from the incident on April 7 shows Moore racing toward the suspect, pushing him onto a bench and holding him down before another staffer helped kick the weapon away.

"I'm glad it worked out the way it did," Moore says in the interview. "Again, I think God's hand was on all of us, but I can't explain why it happened the way it did."

We'll have more of Matt Gutman's conversation with Kirk Moore on that heroic moment — and a special surprise for the principal — Monday on "CBS Mornings."