The 20-year-old man who shot 20 children and six teachers and school employees at Sandy Hook Elementary School in Newtown, Conn. last December, kept among his personal belongings a spreadsheet detailing prior mass murders, internet bookmarks about firearms, documents on weaponry and images of himself holding a rifle to his head.

These chilling details of Adam Lanza’s private life were revealed in a 48-page report about the massacre, published early last week by the Connecticut State Attorney’s Office. The report chronicles the path of Lanza’s 11-minute rampage through the school and sheds new light on Lanza’s personal life, based on possessions found in the Lanza home and interviews with his family and acquaintances. Investigators concluded that Lanza acted alone in the shooting, but could not establish a clear motive for his actions.

“The evidence clearly shows that the shooter planned his actions, including the taking of his own life,” State Attorney Stephen Sedensky III wrote in the report’s executive summary. “But there is no clear indication why he did so, or why he targeted Sandy Hook Elementary School.”

The first victim of Lanza’s killing spree was his own mother, with whom he lived at 36 Yogananda St., located about 5 miles away from Sandy Hook Elementary School. The investigation found that Lanza shot his mother, Nancy, while she was asleep in her bed before driving to the school. Investigators later found that “someone” heard two or three gunshots in the area of the house between 8:00 a.m. and 9:00 a.m.

At approximately 9:35 a.m., Lanza — armed with several handguns and long-guns and extra ammunition — shot his way into the locked school building. Wearing yellow earplugs, sunglasses and a hat, Lanza walked down the hallway and fatally shot the principal, Dawn Hochsprung, and Mary Sherlach, the school psychologist, who had entered the hall in response to the sound of gunshots. Hochsprung, who was 47 years old, yelled at her colleagues to “stay put” in one of the school’s conference rooms before leaving to investigate the commotion.

Lanza continued to fire throughout his march down the main hallway, wounding two other staff members. He then briefly entered the school’s main office, but left without harming the several staff members who had been hiding there at the time.

Though Lanza’s exact path from the office is not clear, he soon entered two first-grade classrooms, rooms 8 and 10, where he shot 20 students and four adults.

At 9:40 a.m., just five minutes after his forced entry into Sandy Hook Elementary, the shooter committed suicide with a pistol in classroom 10.

According to the timeline laid out by the report, the first officer dispatched by the the Newtown Police Department arrived on school grounds within four minutes of the first 911 call, roughly one minute before Lanza committed suicide. Just last Tuesday Connecticut Superior Court Judge Eliot Prescott ordereds that tapes of the 911 calls placed that morning be made public by Dec. 2.

The report states that Lanza suffered from various mental and social difficulties, but it does not conclude whether they played any role in his decision to attack the school and its students.

“It is known that the shooter had significant mental health issues that affected his ability to live a normal life and to interact with others, even those to whom he should have been close,” the report stated. “What contribution this made to the shootings, if any, is unknown.”

Investigators focused their efforts on the elementary school and Lanza’s bedroom. Lanza’s weapons, gathered at the school, included a Glock handgun and a Bushmaster rifle. In Lanza’s bedroom, investigators found that Lanza had smashed one of his hard drives, from which no information could be recovered.

Investigators found one video game entitled “School Shooting,” in which the user controls a character who shoots at students in a school, installed on Lanza’s computer. Lanza had also saved internet pages related to firearms, military and mass murders and a series of images of himself holding guns to his own head.

“A review of the electronic evidence that appeared to belong to the shooter revealed that [he] had a preoccupation with mass shootings, in particular the Columbine shootings,” the report said.

Interviews with Lanza’s acquaintances revealed contradictory information about his social interactions and relationships with others, the report stated. Some people said that Lanza could be humorous, while others characterized him as “unemotional, distant and remote.”

Several teachers and neighbors who observed Lanza in his early- to middle-childhood years described him as a quiet and smart child who, in many ways, seemed completely normal. He was an average student and was friendly towards others, one of his sixth-grade teachers recalled.

But in the years leading up to the attack, Lanza appears to have become increasingly reclusive, as he would isolate himself in his bedroom and limit his communication with others. By the time he reached high school, he had dropped out of several school activities, including the band and the soccer team.

In a statement posted on her official blog, Newtown First, Selectwoman Patricia Llodra said that she had hoped to see a motive identified in last Monday’s report, but acknowledged that the report did shed new light on the case.

“Much of the detail in the report is presented in such a factual, neutral way that it almost felt unreal, sanitized, somehow,” Llodra said in the Nov. 26 post, the blog’s most recent. “I was hoping to find more answers to why Adam acted out his anger and confusion on Sandy Hook School and am disappointed to be left still wondering.”

Llodra also lamented that Lanza’s mental illness left him “damaged beyond reach.”

Criminologist Grant Duwe, director of research and rvaluation at the Minnesota Office of Corrections, who studies patterns in mass public shootings, said that, while most people respond to shootings with calls for tighter gun control, lawmakers should pay greater attention to mental health as well. Of the approximately 160 mass shootings that have taken place in the U.S. since 1915, 60 percent were committed by people who had demonstrated serious mental illness before their attack, Duwe said.

“This doesn’t mean that someone who has a mental illness is about to commit a mass public shooting, but it suggests that it can be a risk factor,” he said.

The Connecticut State Police Department is due to release a separate report into the investigation soon.