A teenage girl is accused of attacking two students with a hammer at Columbine High School in Littleton, Colo.

According to an AP report, the teenage girl had warned a school employee of the attack moments before it happened.

 Jefferson County School District security director John McDonald says investigators Monday were trying to gather additional details.

McDonald says the 14-year-old suspect targeted a 15-year-old girl in a bathroom. A male student saw the attack developing and was injured while stopping it.  

The Littleton high school was the scene of one of the worst school attacks in U.S. history. Students Eric Harris and Dylan Klebold opened fire on April 20, 1999, killing 12 classmates and a teacher and wounding 26 others before killing themselves in the school's library.