A string of innocuous choices made by an Oregon father brought him to the elementary school where he killed a mass shooter in an act he believed would be his last.

Police have credited the quick thinking and decisive action of Bend carpenter Kaylub Giamanco for confronting 16-year-old Griffin J. John II and stopping the teen shooter’s carnage on Oct. 15.

The gunman had already killed a teacher and three young children at Silver Rail Elementary School and could have continued his attack had Giamanco, 36, not randomly ended up at the crime scene.

In an emotional and harrowing interview with Oregon Public Broadcasting published on Friday, Giamanco recalled that fateful day.

“I’ve always wanted to change the world, but I’ve felt small. I’m just a carpenter from Bend, Oregon. I was a nobody other than to my friends and family,” he told OPB.…