"She has made some concerning comments in the past. and because of that we were concerned", he said.
The FBI's Rocky Mountain Safe Streets Task Force issued a notice describing Pais as "infatuated with (the) Columbine school shooting".
Pais was last seen in the Jefferson County foothills and is considered extremely unsafe.
"She can, please, come home".
Tuesday's lockout, less serious than a public safety "lockdown", means activities inside schools may continue as usual but entry and exit are restricted, the Jefferson County Sheriff's Office said on Twitter.
He said he had no other information.
Authorities said they have not identified any connections she has with Colorado and most of her threats were spoken. They say she should be considered armed and extremely unsafe.
A student leaves Columbine High School late Tuesday, April 16, 2019, in Littleton, Colo.
The FBI said Sol Pais, 18, is "considered to be extremely dangerous" and "made threats to commit an act of violence in the Denver metropolitan area" just days before the 20th anniversary of the attack that killed 13 people.
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.
Davis says "Troubled kids in our schools, and nobody knows about it. the teachers and administrators are the first line. they need to see that, and they need support and help".
Authorities said they are being especially cautious because Pais' statements don't express a specific plan and were mostly spoken.
The Jefferson County Sheriff's Office said Pais traveled to Colorado Monday night and made threats.
Jefferson County comprises the area to the west of Denver and includes cities Golden, Lakewood, and others.
All after-school activities, sports and practices will occur as normal except for at Columbine High School, where after-school activities are canceled.
The students walked to crosswalks and buses parked near the entrance. All students were safe, school officials said.
Jenny Fulton, another sheriff's spokesperson, said the FBI was investigating the apparent threat. The massacre was the deadliest school shooting in American history at the time.
"We always have heightened awareness close to high-profile anniversaries like this", Billinger said. "But we do intend to make sure we are engaged with school superintendents and specifically with the Jefferson County School District and the Jefferson County Sheriff's Office and others and with our law enforcement partners to make the very best decision".
She then bought a pump-action shotgun "immediately" upon arriving in Colorado. Extra precautions were taken at schools near Columbine, where sheriff's deputies were on hand.
At 9:20 a.m. this morning, when all was calm, the Jefferson County Sheriff's Office tweeted out the photo below of the Columbine memorial in association with a roster of events associated with the tragic remembrance scheduled for this week.