Propped door provided access to student gunman, police say

Police say the 18-year-old student who opened fire at Arapahoe High School in Centennial, Colo., entered through a door that should have been locked but rarely was. The Denver Post says Arapahoe County Sheriff Grayson Robinson told reporters that the exterior door through which Karl Pierson entered the school had been left propped open. But he added that a locked door likely would not have deterred Pierson. The gunman shot a fellow student to death on Dec. 13 before taking his own life.