School officials later tweeted that all students and staff are safe and students will be released on a normal schedule.
Update 1:10 PM ET: "We can confirm there is investigative activity around the base of Mt. Evans".
Authorities have not provided any additional information at this time.
Doors were locked at Columbine and at least over 20 other schools in the Denver area as the sheriff's office said it was investigating a possible threat against schools that was related to an FBI investigation.
Agents and officers quickly realized Pais had boarded a plane to Colorado, and purchased a weapon there.
After receiving threats, several schools, including Columbine High School, were placed on lockout on Tuesday.
The Miami Herald reported that a man answered the door at her address Tuesday night and identified himself as her father.
Junior David Eaton told the newspaper that he was in a math class when the school announced the lockout. It's not clear where she came from.
While the State of Colorado requires that purchasers of firearms submit to a background check, the process typically takes about fifteen minutes. They called her "extremely risky".
Polis is referring to Sol Pais.
She is from Surfside, Florida in the Miami area and had flown into Denver International Airport Monday.
"What we want to avoid is saying we don't think this person means it", Nicoletti said.
He says Colorado's "biggest priority is keeping our children safe". It's "not the first threat" to involve or reference Columbine, he said, and "I know that this opens a wound especially on an anniversary week".
Sol Pais, 18, flew to Denver from Miami and bought a pump-action shotgun and ammunition, said Dean Phillips, special agent in charge of the Federal Bureau of Investigation in Denver.
"It's a credible threat. but she did not make it directly", said Jenny Fulton, a spokeswoman with the sheriff's office.
Schools in the USA city of Denver closed amid fears that an armed woman obsessed with the Columbine High School massacre 20 years ago poses a "credible threat". Jefferson County Sheriff's Office tweeted a picture of 18-year-old Sol Pais and asked people to keep an eye out for her.
Pais has no specific known connections to Colorado, Phillips said.
Saturday marks 20 years since the shooting at Columbine High School, where two students killed 12 classmates and a teacher in 1999.
"She is a white female, 18 years old, approximately 5'5" in height with brown hair. Authorities said she was armed and "considered to be extremely risky".
All classes and extracurricular activities for about a half-million students were canceled as a precaution.
Education officials say Denver-area public schools will be closed Wednesday due to an ongoing safety concern as authorities search for a woman who they say is armed, making threats and "infatuated" with the Columbine High School shooting.
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