A young woman who is "infatuated" with the 1999 shooting at Columbine High School and made gun threats - just days before the 20th anniversary - is being hunted by the FBI.
Sol Paris flew to Denver, the location of the school massacre, from Miami and bought a pump-action shotgun and ammunition, Dean Phillips, of the FBI in Denver, said.
The 18-year-old threatened Columbine and several other high schools outside Denver.
The undisclosed threats led the schools to go into lockdown for nearly three hours.
All students were safe, school officials said.
Pais was last seen in the foothills west of Denver, and was considered armed and extremely dangerous and should not be approached.
The Columbine school massacre killed 13 people.
The FBI’s Rocky Mountain Safe Streets Task Force issued a notice on Tuesday describing Paris as “infatuated with (the) Columbine school shooting”.
The alert also said police who come into contact with her should detain her and evaluate her mental health.
Mr Phillips said the threats she made were general, not specific to any school.
“She has made some concerning comments in the past… and because of that we were concerned,” he said.
The doors were locked at Columbine and more than 20 other schools in the Denver area as the sheriff’s office said it was investigating threats against schools related to an FBI investigation.
Columbine students continued attending classes in the afternoon and left school on time, but after-school activities were cancelled on the campus in Littleton, Colorado.
Pais' threats came just four days before the 20th anniversary of the Columbine school shooting.
Teenage gunmen attacked Columbine on April 20 1999, killing 12 classmates and a teacher.