On Friday afternoon, 18-year-old Karl Pierson walked into his Centennial, Colo., high school with a shotgun, a machete, and Molotov cocktails with the intent to kill his former debate coach and as many students as possible. Some 80 seconds later he killed himself after critically wounding two students (one critically) and starting a small fire in the school library.

Much of the credit for limiting the carnage from Pierson’s attack on Arapahoe High is being lauded upon an Arapahoe County Sheriff’s deputy who serves as the school’s resource officer.

The deputy was yelling for people to get down and identified himself as a county deputy sheriff, Arapahoe County Sheriff Grayson Robinson told CNN. "We know for a fact that the shooter knew that the deputy was in the immediate area and, while the deputy was containing the shooter, the shooter took his own life."

He praised the deputy's response as "a critical element to the shooter's decision" to kill himself, and lauded his response to hearing gunshots. "He went to the thunder," he said. "He heard the noise of gunshot and, when many would run away from it, he ran toward it to make other people safe."