A series of graffiti threats led school officials to lock down Columbine High School in Littleton, Colo., for a day and implement precautionary security measures..

According to Jacki Tallman, spokeswoman for the Jefferson County Sheriff’s Office, the school received a "nonspecific" message that "harm may come to others."

In lockdown status, students must remain in the school building until the end of the day. "This is really a precautionary step. We believe that we are far enough in the investigation that nothing will happen," said Rick Kaufman, school-district spokesman.

Extra security officers and sheriff’s deputies were posted at the school and staff members monitored doors.

Columbine High School is where students Eric Harris and Dylan Klebold fatally shot 12 students, one teacher and themselves in an April 1999 school shooting.