The Jefferson County Sherriff's Office today confirmed an 18-year-old woman named Sol Pais travelled to Colorado and made threats that sparked the lockdown.
In addition to Denver Public Schools, which serves almost 100 000 students across roughly 200 schools, numerous other school districts said they would not open on Wednesday as a precaution.
Jefferson County Sheriff's Department tweeted about the lockdown mid-afternoon Tuesday.
Columbine High School and about a dozen other schools are on lockdown as law enforcement says it is investigating what appears to be a credible threat possibly involving the schools.
The Department of Public Safety urged schools urged schools to tighten security, and more than 20 put lockdowns in place.
Almost 20 years ago, two students, Dylan Klebold, 17, and Eric Harris, 18, killed 12 students and one teacher in a mass shooting at Columbine. Authorities requested the lockout in Jefferson County on Tuesday afternoon as they searched for the suspect, whose description was released on Twitter with a warning not to approach her.
"Please do not approach her as she is considered armed and unsafe".
Jefferson County comprises the area to the west of Denver and includes cities Golden, Lakewood, and others.
Officials didn't provide further details about the threats or say where she was from.
Students left classes on time, but after-school activities were canceled at Columbine in Littleton, Colorado.
"There are many people that work diligently day in and day out. that are making the very best decisions they can for the sake of the kids who are in schools each and every day", said Jefferson County Sheriff Jeff Shrader.
The students walked to crosswalks and buses parked near the entrance.
Jenny Fulton, another sheriff's spokesperson, said the FBI was investigating the apparent threat.
Her relatives say, if the allegations are true, there may be problems they couldn't see on the surface.
Officials had no answer at the time of the press conference as to whether schools would open on Wednesday.
CBS Miami reports Pais' family is asking her to turn herself in. Two threats were made to the school: one call said there was a bomb inside the building, another said there was a person with a gun outside of it. There was no immediate indication whether there was any connection to the anniversary.
Authorities announced late Tuesday they would be closing all Denver schools on Wednesday.
Federal Bureau of Investigation agents, along with Jefferson County Sheriff's deputies and Colorado state troopers, have searched for her, including hunting through rural Jefferson County foothills throughout the day and have published her name and photo in local media.
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