A 48-page long report on the investigation into the Sandy Hook Elementary School massacre was released on Monday.

The report, issued by Connecticut’s Division of Criminal Justice and lead investigator, State Attorney Stephen Sedensky III, states that the shooter entered the school on Dec. 14, 2012 with a with a Bushmaster Model XM15-E2S rifle and first shot and killed the principal and school psychologist. Police arrived at the crime scene four minutes after the first 911 call was received at 9:35 a.m. by the Newtown Police Department, and one minute later, the shooter — identified as 20 year old Adam Lanza — had taken his own life with a hand gun.

On the day of the tragedy, police thought there may have been multiple shooters involved, but the State attorney concluded that the shooter acted alone and was solely responsible for the shooting of 20 first grade students and six adults.

“None of the evidence developed to date demonstrates probable cause to believe that any other person conspired with the shooter to commit these crimes or aided and abetted him in doing so,” the report states.

The report does not answer the crucial question of what motivated Lanza to murder twenty seven people, including his own mother, whom he shot in the morning before driving to Sandy Hook.

The report says that Lanza had significant mental health issues, as he was diagnosed with Aspergers in 2005, but offers no suggestion of whether Lanza’s health problems may have contributed to the shootings.

“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 report states.

Interviews with Lanza’s friends and classmates revealed contradictory information about Lanza’s behavior: while some said that Lanza was bullied as a child others “saw nothing of the sort,” and while some considered the shooter humorous, others referred to him as “unemotional, distant and remote.”

Monday’s release is only a small part of the collection of evidence contained in a several thousand-page file belonging to the Connecticut State Police, according to the Associated Press. The report does not include a recitation of the 911 calls made from inside the school, nor does it provide information from witnesses who were in the classrooms.