** FOR USE AS DESIRED WITH ANNIVERSARIES** FILE ** Unidentified students embrace each other at a makeshift memorial for their slain classmates at Columbine High School on a hilltop overlooking the school in Littleton, Colo., in this April 24, 1999, file photo. Twelve students and a teacher were killed in a murderous rampage at the school on April 20,1999, by two students who killed themselves in the aftermath. (AP Photo/FILE/Bebeto Matthews)