An 18-year-old who authorities say had an "infatuation" with the 1999 Columbine High School massacre appears to have kept a journal online in which she wrote about suicide and guns, and alluded to "plans" she was making.

Officials said the teen, Sol Pais of Florida, flew from Miami to Colorado earlier this week, bought a pump-action shotgun and ammunition upon arrival and then disappeared off of their radar, prompting a massive manhunt. On Wednesday, officials said she had been found dead.

"There is no longer a threat to the community," the FBI in Denver confirmed in a tweet. Jefferson County, Colorado Sheriff Jeff Shrader later said the FBI had found Pais dead from an apparent self-inflicted gunshot wound.

Sol Pais, using the handle "Dissolved Girl," appeared to post photos of herself and journal entries to a personal blog. Obtained by NBC News

In an apparent journal signed with her full name — which law enforcement has not confirmed belongs to her — Pais appears to describe feeling miserable and out of place, along with having thoughts of suicide and a desire to procure weapons. The journal entries are dated June 2018 through March 30, 2019.

“I wish I could get a gun by the end of the summer," one entry reads.

Other entries reference plans being made. Another shows drawings of one of the Columbine gunmen, Dylan Klebold.

"Had a dream last night about the future and it was eye opening. Was only a week away from the day and I had my [expletive] shotgun...” an entry reads, a possible reference to the anniversary of the Columbine massacre.

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Investigators say Pais was obsessed with the shooting at Columbine High School that left 12 students and a teacher dead 20 years ago this week and said on Tuesday evening that she posed a "credible threat" to the Denver-area community and schools.

A journal entry apparently written by Sol Pais and uploaded to a personal blog. Obtained by NBC News

"Because of her comments and her actions, because of her travel here to the state, because of her procurement of a weapon immediately upon arriving here, we considered her to be a credible threat — certainly to the community and potentially to schools," Dean Phillips, FBI special agent in charge of the Denver field office, said at a press conference.

"She has had an infatuation with Columbine and the perpetrators of Columbine," he added. "She has made comments to that effect, but she hasn't identified a specific threat to a specific school."

After receiving word of the FBI investigation on Tuesday, more than 20 schools, including Columbine, went on lockout — meaning exterior doors were locked due to a threat outside, but all scheduled classes and activities inside were held as they normally would be.

Colorado's Department of Education announced on Twitter that all Denver metro area school districts were closed on Wednesday due to "ongoing safety concerns."

While it was not clear whether Pais wanted to cause harm to Columbine specifically, criminal justice experts say it is likely not a coincidence that she flew to Colorado days ahead of the 20th anniversary of the massacre there if she was infatuated with the shooting.

Copycat shooters or wannabe shooters often become obsessed with the date of a tragedy that they hope to emulate, said Clint Van Zandt, a former FBI criminal profiler and NBC News senior criminal analyst.

"You have invested so much of yourself in that," Van Zandt said. "Your fantasy, your personal delusion around that — you incorporate that with the actual event itself, and you become part of the event, the event becomes part of you."

"For some, psychologically, it could demand that they do [a copycat attack] on that date because you spent so much time studying that date and you believe that you will get more attention for having done it," he added.

Law enforcement typically beef up staffing and surveillance ahead of big anniversaries such as this one, said Tod Burke, a former Maryland police officer and criminal justice expert. He said authorities will comb social media for any red flags and add extra protective patrol, both undercover and visible to "let the people know that law enforcement is out there."

Both Van Zandt and Burke said that while there is not necessarily a typical profile of a mass attacker, Pais stands out as a young woman who appeared to be working on her own.

But they said she is hardly the only plotter to be obsessed with Columbine, something that numerous attackers since have referenced in confessions as their blueprint.

Burke said Columbine was a turning point in the amount of attention it drew.

"It was one of the first that was captured live on TV, so we watched it play out. Not many incidents prior to that can we say that," he said.