In all of the evidence gathered from Adam Lanza's home in Newtown, Conn., which ranged from the banal to the bizarre, officials were unable to pull out a motive for his rampage through Sandy Hook Elementary School last December.
If history is any guide, profilers and researchers will spend years picking apart the chimeric remnants of Adam Lanza's personality that might somehow, someday provide an explanation.
There were clues as to tastes and habit that revealed a labyrinthine personality seemingly at odds with itself: the mind of a boy concerned about staying thin, who obsessed both over mass killers and playing the music video game Dance Dance Revolution.
Lanza's digital files included both photos of Legos as well as photos of himself holding guns up to his own head, according to investigative files released by Connecticut officials Monday. There there was a Word document "explaining why females are selfish," chats related to "homosexual fantasies" and multiple materials related to pedophiles, including a "screenplay or script describing a relationship between a 10-year-old boy and a 30-year-old man."
Lanza was 20 on the day of his rampage at the school that left 20 children and six adults dead, and there was plenty of evidence collected by investigators at the home he shared with his mother in Newtown.
Yet investigators found no manifesto; no goodbye tell-all to explain specifically why Lanza would embark on the deadliest school shooting since the Virginia Tech massacre in 2007.
But of all the odd and dark surprises contained within the Lanza home on Yogananda Street, where he killed his mother, Nancy, before making his way to the school, at least one finding that caught investigators' attention was a familiar one: Lanza was fascinated by the 1999 Columbine High School massacre.
And not just fascinated -- Columbine marked the center of his "obsession" with mass shootings, investigators said.
Lanza had "hundreds of documents, images, videos pertaining to the Columbine H.S. massacre including what appears to be a complete copy of the investigation," according to the Newtown report.
Lanza had downloaded several videos about the Columbine killers, Eric Harris and Dylan Klebold, who shot to death 12 fellow students and a teacher before shooting themselves. It was then the worst school shooting in U.S. history.
And Lanza didn't just passively consume: He had posted on a blog that was dedicated to mass shootings and Columbine in particular, investigators said.
This likely adds another chapter to a grim thesis held by some researchers: that 14 years later, the Columbine massacre still serves as a master script of nihilistic, spectacular violence for other shooters to follow.
In an analysis of school rampages between 1999 and 2007, Professor Ralph W. Larkin of the John Jay College of Criminal Justice at City University of New York found that eight out of 12 shooters "directly referred to Columbine."
Consider Seung-Hui Cho. Shortly after the Columbine shooting, when Cho was in eighth grade, he was said to have written a disturbing report for his English class in which he said he wanted to "repeat Columbine," according to investigators.
Eight years later, Cho went on a rampage at Virginia Tech University that left 32 people dead, far surpassing the body count at Columbine -- but not before Cho sent ramblings to the media in which he referred to himself as a "martyr" seeking revenge like "Eric and Dylan," the Columbine shooters.
And like Eric Harris and Dylan Klebold -- and Adam Lanza, and several other mass shooters following a similar trope -- Cho killed himself at the end of the attack.
Columbine's massacre may have taken place in suburban Colorado, but it shocked America. The touchstones for school violence suddenly changed, with students all over the country more likely to report feeling too unsafe to go to school.
In the 50 days after the Columbine shooting, Pennsylvania school districts, for example, reported receiving 354 threats of school violence -- "far exceeding the 1 or 2 threats per year estimated by school administrators before 1999," according to one analysis.
The threats eventually diminished, but Columbine's influence had far from disappeared.
And that's just in the U.S.
"Rampage shootings since Columbine have gone international, with school shootings modeling Columbine in Canada, Sweden, Bosnia, Australia, Argentina, Germany and Finland," Larkin, the John Jay professor, wrote in American Behavioral Scientist in 2009. "Prior to the Columbine shootings, the only other country to have experienced rampage shootings was Canada," in 1975 and 1989. (Six out of 11 shooters in non-U.S. school rampages referenced Columbine, Larkin reported.)
The fear among some researchers and media critics has been that Columbine set a template for one-upsmanship that is enabled by a 24/7 media that can encourage other would-be killers.
"Records exist but to be broken," one criminologist warned darkly in 2007 after criticizing the "nearly gleeful enthusiasm" of on-air anchors reporting that Virginia Tech had become the deadliest campus massacre on record.
Dave Cullen, a journalist who spent 10 years covering and researching the Columbine shooting before publishing what is widely considered the definitive book on the attack, noted that there had been other school shootings in the 1990s. Columbine, though, set a new tone.
"For various copycats, Columbine sort of ratcheted up the goal of what it took to be covered," Cullen told the Los Angeles Times. "I feel very strongly that we the media have become complicit. … We keep score."
Perhaps Lanza was aware. One of the things police discovered at his home was a spreadsheet. It was a detailed list of mass killings.