She was last seen in the foothills in Jefferson County and is wearing a black T-shirt, camouflage trousers and black boots.
Denver area schools, which were closed on Wednesday while Federal Bureau of Investigation agents, Jefferson County deputies and Colorado state troopers searched for Pais, were expected to reopen on Thursday with mental health counselors standing by. The station said that police officers rushed to the scene after reports of a naked woman with a gun running through the woods.
"There is no longer a threat to the community", the FBI Denver field office tweeted earlier.
The FBI said Pais flew to Colorado Monday night and bought a pump-action shotgun as well as ammunition.
In Pais' hometown, Surfside Police Chief Julio Yero asked that the family be given "privacy and a little time to grieve".
Pais was reported missing by her parents on Monday night.
Students leave Columbine High School late in Littleton, Colo., on April 16, 2019.
Another classmate, 17-year-old junior Drew Burnstine, said Pais was a quiet, smart student who sat alone in class and "never caused problems or indicated that she wanted to harm anyone".
"We have no specific information about any specific threat to any specific school".
Dozens of Denver schools were closed Wednesday as police searched for Pais who was eventually found in Littleton.
Schools in the Denver area were shut down Wednesday because of the threats.
The incident came just days before the 20th anniversary of the Columbine massacre, which happened when two teenagers went on a killing spree at Columbine High School, killing 12 students and 1 teacher before they committed suicide.
Dean Phillips, the special agent in charge of the FBI's Denver office, said Pais had made comments in the past that expressed "an infatuation" with the Columbine massacre and its perpetrators.
Galterio graduated from Columbine High School in 1992 and she wept as she recounted how she's taken her child to the Columbine Memorial to pay respects "on a regular basis". Saturday, April 20 marks the 20th anniversary of the Columbine tragedy, in which two students opened fire and killed 13 people.
Pais had apparently logged some of her thoughts in various journal entries, replete with nods to her favorite music (Nine Inch Nails to Smashing Pumpkins) and doodles of firing guns and blood-dripping knives.