"They have found Miss Pais deceased from an apparent self-inflicted gunshot wound," said Jefferson County Sheriff Jeff Shrader, whose jurisdiction includes Columbine High School in Littleton, Colorado. "I don't believe that they were in active pursuit at the time she was found dead."
Pais hadn't made any specific threats, but police had said she was potentially dangerous and was obsessed with the April 20, 1999, Columbine High School massacre in Littleton that left 12 students and a teacher dead.
She bought a shotgun and ammunition from a gun shop near Littleton just days before the 20th anniversary of the shooting this week, authorities said. After traveling to Denver she went directly to the store to buy the weapon, an FBI official said.
Hundreds of schools, with more than 400,000 students in and around Denver, canceled classes on Wednesday, because of the potential threat, officials said. That represented nearly half of Colorado's 911,000 public school students, officials said.
"I'm very thankful this threat is over," said John McDonald, executive director for security and emergency management for Jefferson County Public Schools.
"But we know Columbine continues to attract people from around the world. And if I have any message: We are not a place to come visit if you're not a student. If you don't have business there, we're not a tourist attraction and we're not a place for you to come and gain inspiration."
McDonald described Pais' journey to Colorado as a "pilgrimage."
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"We are used to threats, frankly, at Columbine," McDonald said. "This one felt different. It was different. It certainly had our attention."
Dean Phillips, FBI special agent in charge of the Denver field office, said at a news conference Wednesday that Pais’ body was found between 10:30 a.m. and 10:40 a.m., and she was last seen in the area on Monday after being dropped off by a "for-rent vehicle." Investigators don’t know why she chose that area, but the driver helped authorities pinpoint her last known location, he said.
Phillips said it appears Pais was alone and killed herself with the shotgun she bought in the Denver area.
Sheriff Shrader told MSNBC on Wednesday, a short time before Pais was found, that every April brings copycat threats to Columbine. But he said Pais' interest in the school stood out.
"We do get a number of threats each April that come up and, obviously, with Columbine having its 20-year anniversary, it perhaps heightened some of those sensitivities," said Shrader, who was with his department back in 1999 when the mass shooting happened.
"And in terms of the decision-making process, once it was learned the general nature of some of the comments that this person had made, coupled with buying a gun and coupled with this being the Columbine week and her fascination with it ... school superintendents were on a phone call late last night and they came to the conclusion that it would be best for their school districts if they closed schools today."
Pais apparently kept an online journal signed with her full name and described how she felt miserable, along with thoughts of suicide and desire to gain weapons. The journal is dated June 2018 through March 30, 2019.
“I wish I could get a gun by the end of the summer," according to one entry.
She also made a drawing 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 shooting anniversary.
Police and FBI agents had been looking for Pais, with orders to detain her for a mental health evaluation, authorities said. She was last seen wearing a black T-shirt, camouflage pants and black boots, officials said.
In Pais' hometown of Surfside, Florida, Police Chief Julio Yero thanked the woman's family for their help in the search.
"This family contributed greatly to this investigation from the very onset," Yero said. "They provided valuable information that led us to Colorado and a lot of things that assisted in preventing maybe more loss of life."
In a brief interview with NBC Miami on Tuesday night, Pais father had begged his daughter to come home. He said the search for her had taken an emotional toll on the family.
"It's like a bad dream," he said. "We don't know, we don't have any idea."
Phillips, the FBI special agent in charge, said the investigation is ongoing.
"The reason that we do that is we are trying to follow every lead, assess every social media outlet — everything that she may have done over the last several months to a year, to ensure that there are no accessories, that there are no accomplices that might be working with her,” Phillips said. "It's very important for us to ensure that there is no further threat to the Denver community.”
Phillips also called the cooperation between federal and local law enforcement agencies “incredible” and said Wednesday "it was a long night."
"The partnerships during this investigation, this trying 36 hours, was incredible," he said. "The federal partners, the state partners, the local partners all came together in an incredible manner and worked tirelessly to put this to bed," he said.
David K. Li
David K. Li is a breaking news reporter for NBC News.
Pete Williams is an NBC News correspondent who covers the Justice Department and the Supreme Court, based in Washington.