Adam Lanza, the Sandy Hook Elementary School shooter, was obsessed with the Columbine shooting, according to a report released Monday.
The findings outline Lanza's mental state and his antisocial behavior before the shooting.
He was a video game addict that had a collection of guns. Lanza was isolated in his room, where he spent hours with the windows taped with plastic, refusing to allow anyone inside.
He kept videos of suicides by firearms and kept newspaper articles about violence against children. His drawers were filled with ammunition.
Lanza had apparently communicated with a boy in Texas through an online video game, telling him that there would be a school shooting the next day.
Although he lived in the same house as his mother, Nancy Lanza, he would only communicate with her through email.
Despite Lanza's mental state, his mother appeared to encourage his relationship with firearms.
The weapons Lanza would later use in the killing had all been purchased legally by his mother.
The day of the shooting he shot and killed her using a .22-caliber rifle.
After killing his mother Lanza entered the Sandy Hook Elementary School with a Bushmaster rifle, a Glock 10-millimeter pistol, a Sig Sauer 9-millimeter pistol and a "large supply of ammunition."
One hundred and fifty four shots were fired in under five minutes using the semi-automatic weapon.
The Dec. 14, 2012 shooting saw 20 first-graders and six school employees shot dead.
The only thing considered missing from the report was a clear motive.
The author wrote: “The evidence clearly shows that the shooter planned his actions, including the taking of his own life, but there is no clear indication why he did so, or why he targeted Sandy Hook Elementary School.”
The shooting raised calls in Congress for stricter gun control laws - calls that have since gone silent despite numerous other mass shootings that have occurred in the meantime.