Connecticut authorities said they planned Friday to release state police documents from the investigation into last year's Newtown school massacre.
State police said their report totals several thousand pages. The report "has been redacted according to law," and includes text, photos and 911 calls received by state police, they said Thursday.
Prosecutors issued a summary of the investigation last month that portrayed the gunman, Adam Lanza, as obsessed with mass murders, but the report concludes that Lanza's motives for the massacre might never be known.
Lanza gunned down 20 first-graders and six educators with a semi-automatic rifle at Sandy Hook Elementary School on Dec. 14, 2012, after killing his mother inside their home. He committed suicide with a handgun as police arrived at the school.
The summary says the 20-year-old Lanza had "significant mental health issues."
The report said that in 2005, Lanza was diagnosed with Asperger's disorder, a mild form of autism that is not associated with violence, and that he lacked empathy for others and behaved strangely. Nobody was allowed into his room, he wouldn't touch doorknobs, his food had to be arranged on the plate in a certain way, and he changed clothes often during the day, according to the report.
In fifth grade, Lanza wrote "The Big Book of Granny," in which the main character has a gun in her cane and shoots people and another character talks of liking to hurt people, especially children. The book was among items seized from Lanza's home, but there was no indication he ever handed in the book at school.
Lanza became obsessed with the 1999 bloodbath at Columbine High in Colorado and other mass killings, the report said. He even kept a spreadsheet ranking mass murders.