Story highlights Carter Peterson died Sunday night

"I dropped to my knees," the firefighter said

(CNN) It's every parent's worst nightmare, but it was even worse for Randy Peterson.

The volunteer firefighter from Ada, Minnesota, was rushing to a fiery car crash and desperately trying to reach his 16-year-old son, Carter. That was Peterson's routine whenever he got called to an emergency and knew one of his children wasn't home.

Peterson called and called but got no answer.

When he got to the scene of the crash Sunday night, he knew why.

"Seeing the car on fire and the rims, I knew," Peterson told the Minneapolis Star Tribune. "I dropped to my knees. I was a mess. Another member of the crew just held me."

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