The safety unit run by Jefferson County Public Schools is considered one of the most sophisticated school security systems in the country.
On April 20, 1999, a pair of students rampaged through Columbine High School, murdering 12 of their classmates and a teacher and wounding 24 before killing themselves. Phillips said that would not prevent authorities from apprehending Pais.
"Please do not approach her as she is considered armed and unsafe".
Saturday will mark 20 years since the massacre at the Denver-area school.
Patricia Billinger, a spokeswoman for the Colorado Department of Public Safety, says the agency made the recommendation because Tuesday's threat was deemed "credible and general". As the district prepares for the day's memorial events, it is fending off an onslaught of curious strangers who trespass in the parking lot of the high school - sometimes more than 30 people in a single day.More news: Georgia Engel Dead - 'Mary Tyler Moore Show' Star Dies at 70
Aurora Public Schools, east of Denver, said all of its schools were "placed in secure perimeter".
Colorado's Columbine High School and at least 20 surrounding schools were placed under a "lockout" security alert on Tuesday as authorities cited a "potential credible threat" posed by an 18-year-old woman described as armed and "extremely unsafe".
She is described as an 18-year-old white female from Florida last seen in the area wearing camouflage pants, a black t-shirt and black boots. "She never got in trouble", she said.
Officials have said Pais was "infatuated with (the) Columbine school shooting" and should be considered "armed and extremely dangerous".More news: Apple Spending Over Half A Billion on New Gaming Service
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.
Classes continued as normal at most of the affected schools, except for Columbine, which canceled after-school activities.
A student leaves Columbine High School late Tuesday, April 16, 2019, in Littleton, Colo. All students were safe, school officials said. The students walked to crosswalks and buses parked near the entrance.
A spokesman for the Jefferson County Sheriff's Office, Mike Taplin, said the lockdowns involved an FBI investigation but he couldn't provide any details.
Police are searching for an armed and unsafe 18-year-old woman who is "infatuated with Columbine", referring to the school massacre 20 years ago.More news: Islanders top Penguins 4-1 to take 3-0 series lead
CBS Miami reports Pais' family is asking her to turn herself in. There was no immediate indication whether there was any connection to the anniversary. "Children are safe. Deputies are at the schools".
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