A string of innocuous choices made by an Oregon father brought him to the elementary school where he killed a mass shooter in an intervention the dad believed would be his last act on earth. 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. Watch NBC 5 free wherever you are WATCH HERE WATCH HERE The gunman had already killed a teacher and three young children at Silver Rail Elementary School on Oct. 15 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. I feel like if I'm going to have a voice, then I'll be damned if I'm not going to use it to change this world, to make it a better place. Giamanco's presence in the neighborhood near Silver Rail came after a series of seemingly benign decisions the carpenter made that Thursday about lunch. Giamanco packed a mid-day snack but changed his mind about eating it, instead opting to drive home to have leftover tacos with his wife, he said. And on his way home, Giamanco had briefly considered going to a masonry shop to buy some bolts he needed, but again opted to go home for the tacos. Those choices led him to Brentwood Avenue near his children's school just before 1 p.m., where he spotted a man in black with a long gun opening fire on a motorist and a woman mowing the school lawn, he recalled. Giamanco, who kept a .40 caliber handgun in his truck console, saw the killer toss his weapon over the school fence before climbing it himself. The father understood what was happening and that's when panic filled into my brain, and that's when I opened my center console. Giamanco, who has two girls #nbcdfw #crimewatchdallas