Sol Pais, the 18-year-old woman suspected of making threats against Denver-area schools including Columbine, has been found dead, officials said Wednesday. Investigators closed in on the teen Wednesday near the Echo Lake Lodge at the base of Mount Evans in Clear Creek County, CBS Denver reported.

Officials said at a news conference Pais was found dead of an apparent self-inflicted gunshot wound.

Authorities had been tipped off to the campground in the Arapaho National Forest by a rideshare driver who dropped her off there, and federal and local law enforcement teams were waiting until daylight on Wednesday before beginning an expanded search of the area, according to FBI Denver special agent in charge Dean Phillips.

Sol Pais Jefferson County Sheriff

Authorities had been conducting a massive manhunt for the Florida teen they described as "armed and extremely dangerous," saying she was "infatuated" with the Columbine school shooting. The alleged threats led to the closure of school for more than half a million students on Colorado's Front Range Wednesday. The threats came days before the 20th anniversary of the deadly shooting at Columbine High School, which left 13 students and teachers dead in 1999.

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Pais traveled to Colorado from Miami on Monday night and bought a pump-action shotgun and ammunition shortly after arriving, according to the Jefferson County Sheriff's Office and the FBI.

Pais had apparently made disturbing comments about Columbine to friends and family and on social media, Phillips said, and was reported missing by her parents in Surfside, Florida. Police there said the parents aided in the investigation and provided valuable information that led investigators to Colorado. The FBI field office in Miami alerted Colorado authorities to the possible threat Tuesday morning.

Pais bought three one-way flight tickets on consecutive days, raising alarm bells for investigators.

"These unusual actions caused us great concern," Phillips said.

Phillips said Pais had been in communication with the Colorado gun store where she purchased the weapon before she left Florida. When investigators learned she bought the shotgun, they determined she posed a potential threat, Phillips said.

Josh Rayburn of Colorado Gun Broker said in a Facebook post that Pais legally bought the gun at the chain's Littleton location. He said she passed a background check and staff there "had no reason to suspect she was a threat to either herself or anyone else."

Local authorities said the threat, though credible, was general — not referencing a specific school. Schools reacted quickly, implementing lockout procedures, and late Tuesday night, several districts announced schools would be closed Wednesday. Among them were Denver Public Schools and Jeffco Public Schools, short for Jefferson County, the district that includes Columbine High.

Schools were expected to reopen Thursday with heightened security.

Jefferson County Schools safety director John McDonald said the community is used to threats at Columbine High, but said this one "felt different." He said he considered the threat a serious one because Pais made a "pilgrimage" to the Denver area and purchased a weapon not far from the Columbine campus.

Sheriff Jeff Shrader said Pais had no apparent personal ties to Colorado, only a "fascination with the Columbine area and the horrendous crime that went on there 20 years ago."

"We are not a place to come visit if you are not a student," McDonald said. "We are not a tourist attraction. We are not a place to come gain inspiration."

"Everything that I have heard in briefings does not that indicate she had any assistance... just a fascination with the Columbine area, and the horrendous crime that went on there 20 years again," Colorado sheriff Jeff Shrader says about Sol Pais pic.twitter.com/2Da7HfpxSW — CBSDenver (@CBSDenver) April 17, 2019

CBS News correspondent Barry Petersen reports Pais' writings in her blogs celebrated violence and death. Investigators are continuing to comb her social media and map her activity to determine whether she worked with any accomplices, Phillips said.

McDonald said it was a difficult decision to close the schools, but that the safety of the students and staff was paramount.

"Looking ahead, we are planning on returning to normal school operations tomorrow with heightened safety and security procedures, and ongoing vigilance in the days to come," said Jason Glass, Jefferson County superintendent. https://t.co/fyE29GdlWJ pic.twitter.com/6V60lA7ycH — CBSDenver (@CBSDenver) April 17, 2019

Frank DeAngelis, who had been the principal at Columbine during the massacre 20 years ago, told reporters he was on campus Tuesday when school officials were first made aware of the threat. He said he immediately checked in on the about 15 staff members who were on campus when the shooting occurred 20 years ago, and then began communicating with families. He described the lockout procedures as being conducted like "clockwork," thanks to the extensive safety training now in place in the years since the massacre.

In 1999, he said, the only drills the school conducted were fire drills.

But now, "the entire time, the kids knew exactly what to do," DeAngelis said. "It was much more reassuring than where we were 20 years ago... the support system is there."

He said the anniversary of the massacre "takes us back."

"You talk to most people that were part of Columbine High School, when that month of April comes around, it does something to us all," DeAngelis said. "But we have that famous saying, 'We are Columbine.' During times like this it resonates, loudly and clearly."