Motive for Colo. School Attack Still Murky

Few details are coming out to possibly indicate why 18-year-old Karl Pierson walked into Centennial, Colo.'s Arapahoe High School with a shotgun, ammunition, a machete, Molotov cocktails, and an intent to kill — but one of his friends has an idea.

Joe Redmond, who had been friends with Pierson for three years, said the teen had an ongoing feud with the school's debate coach, Tracy Murphy, that had escalated.

"Karl had threatened to kill Mr. Murphy," Redmond told The Denver Post .

But Redmond was not clear why.