The shooting at Centennial High School in Centennial occurred just after 9 p.m. . Fabian ##i saw a man armed with a shotgun , running military - style . ` ` We were shaking . We were scared , '' 9th - grader Whitney Riley said . Eric Waugh and his friends thought initially it was an explosion in a chemistry class .
The shooting at Arapahoe High School in Centennial began just after 12:30 p.m. Janitor Fabian Llerenas saw a student armed with a shotgun , running military-style . `` We were shaking . We were crying , '' 9th-grader Whitney Riley said . Eric Waugh and his classmate thought initially it was an explosion in a chemistry class .