Newly released FBI documents in the 2012 Sandy Hook Elementary School shooting paint an even more disturbing portrait of killer Adam Lanza, suggesting his fascination with children verged on the obscene.

Connecticut investigators found a file on Lanza’s computer “advocating pedophiles’ rights and the liberation of children,” a recently unsealed document says. They also reportedly found a screenplay about a relationship between an adult male and a young boy.

There’s no evidence Lanza, 20, acted on sexual interests in young children before the school massacre, which killed 20 elementary school children and six adults before Lanza killed himself.

Lanza’s reclusiveness and proclivity for firearms has been well documented, but the newly released documents offer a fresh glimpse into personality details investigators discovered in the days after the attack. They refer to him as a “shut in” who hadn’t left his home in months, and had likely been thinking about the massacre since March 2011.

“The shooter did not ‘snap,’ but instead engaged in careful, methodical planning and preparation,” the FBI wrote in its analysis. “The shooter was fascinated with past shootings and researched them thoroughly. The shooter shared many similar characteristics and behaviors with other active shooters.”

A woman who had met Lanza online more than two years before the shooting told the FBI that that he once told her sexual relationships between adults and children were “possibly beneficial to both parties.” But he also said they could be “unhealthy,” and never expressed personal sexual interest in children, she said.

Lanza’s thoughts about children went beyond the sexual. The same woman speculated that Lanza slaughtered children to save them from the “brainwashing” and “harmful influences” of adults. Lanza had written on his blog about concerns that teachers and parents exerted too much control over children.

The woman told the FBI that Lanza kept records of hundreds of mass shootings and spent a lot of time on a website dedicated to the 1999 mass shooting at Columbine High School in Colorado. He blogged about his “respect” for mass shooters, recounting a dream he once had in which a student shot fellow classmates for bullying him.

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One person told the FBI that Lanza felt contempt toward the Sandy Hook school because his mother volunteered there, and he felt like she loved the children more than him. Another person told investigators Lanza loved the school and would frequently walk by it.

Lanza’s mother, Nancy, became concerned about him one month before the shooting. She cared for him and bought him the AR-15-style rifle he used in the shooting, one person told investigators, but she wasn’t allowed inside his bedroom. Nancy Lanza, who was among those killed, also rejected recommendations from psychologists that her son be medicated for Asperger’s syndrome, according to the reports.

CORRECTION: Due to an editing error, a previous version of this story said documents indicated Lanza had been thinking about the massacre as early as March 2011, nine months before he acted. In fact, he perpetrated the shooting in December 2012, a year and nine months later.

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This article originally appeared on HuffPost.