The paperwork, photos and videos were heavily blacked out to protect the names of children and to withhold some of the more grisly details of the crime.
Photographs of the home Adam Lanza shared with his mother show numerous rounds of ammunition, gun magazines, shot-up paper targets, gun cases, shooting earplugs and a gun safe with a rifle in it.
The documents also fill in more details about how the shooting unfolded, teachers protected their students and the school janitor confronted the shooter.
Teachers heard janitor Rick Thorn try to get Lanza to leave the school. One teacher, who was hiding in a closet in the math lab, heard Thorn yell, "Put the gun down!" An aide said she heard gunfire and Thorn told her to close her door.
The documents' release marks the end of the investigation into the Dec. 14, 2012, massacre at Sandy Hook Elementary School that left 20 first-graders and six educators dead.
Lanza went to the school after killing his mother, Nancy, inside their home. He committed suicide with a handgun as police arrived at the school.
Prosecutors issued a summary of the investigation last month that portrayed Lanza as obsessed with mass murders, but the report concluded that Lanza's motives for the massacre might never be known.
Lanza "was undoubtedly afflicted with mental health problems; yet despite a fascination with mass shootings and firearms, he displayed no aggressive or threatening tendencies," it said.