article_snippet.sent: the attack took place on the 16th anniversary of the Columbine High School massacre when seniors Eric Harris and Dylan Klebold shot and killed 12 students and one teacher.
article_snippet.sent: The 1999 massacre in Columbine, Colorado, is the deadliest high school shooting in U.S. history.
highlights_snippet.sent: Attack took place on 16th anniversary of Columbine school massacre .