Officials released an image of the woman, identified as Sol Pais, and said she was approximately 5 foot 5 inches, with brown hair.
Amy Meyer, a spokeswoman for the FBI in Denver, said the woman had presented “a threat related possibly to the schools.”
Pais was last spotted in the foothills of Jefferson County, Colorado., authorities said.
The announcement prompted “lockouts,” or heightened security measures, at schools in Jefferson County and the surrounding area. During a lockout, all exterior doors are locked at a school but business continues as usual inside. Police officers aided in end-of-day student release. County officials said that all students and staff members were safe.
During the Columbine High School shooting, on April 20, 1999, two students shot and killed 12 of their classmates and a teacher.
This article originally appeared in The New York Times.