Pais traveled to Colorado on Monday night "and made threats in the Denver metropolitan area", the sheriff's office said in a Facebook post.
Many schools in the Denver area will be closed Wednesday as authorities conduct what they're calling a "massive manhunt" for a young woman they say is "infatuated" with the 1999 shooting at Columbine High School.
On Tuesday, the Jefferson County Sheriff's Office placed Columbine and 21 surrounding schools under a security "lockout", allowing activities inside to continue as usual but restricting entry and exit at the schools.
The threats were credible but not specific, authorities said.
Teenage gunmen attacked Columbine on April 20, 1999, killing 12 classmates and a teacher. 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. They say she should be considered armed and extremely risky.
Students are leaving classes after tightened security at Columbine High School and over 20 other Denver-area high schools after a lockdown caused by a possible threat.
"Any threats involving columbine, or our schools, we take at an elevated rate, so, we're always aware of the situation here", said John Hickenlooper.
At least one school district heeded the advice.
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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.
The Colorado Department of Education encouraged schools in the metro area to go into a lockout and run a controlled release of students at dismissal.
Jenny Fulton, a spokesperson for the sheriff's office, said the Federal Bureau of Investigation requested the sheriff's office assistance with ensuring the safety of the schools.
Officials had no answer at the time of the press conference as to whether schools would open on Wednesday.
The district has also seen an increase in threats and concerning messages, which often come in the form of emails to the school or phone calls to the 24-hour dispatch center run by the district's security team.
A spokesperson for the FBI's Denver field office did not immediately respond to queries.
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.
The Jefferson County Sheriff's Office said deputies were posted at the schools involved. There was no immediate indication whether there was any connection to the anniversary.