NBC News Adam Lanza is seen in this photo obtained and distributed by NBC News. Lanza has been identified as the gunman in the Sandy Hook Elementary School mass shooting in Newtown, Connecticut.

A massive new report from the Connecticut State Police released online Friday reveals new details about the Dec. 14, 2012 mass shooting that took 26 lives at Sandy Hook elementary school in Newtown, Conn.

The 11,000-plus page report includes investigative files, 911 call transcripts, crime scene reports and thousands of photos, among them images of the aftermath of the shooting that show weapons, bloodstains, and bullet-riddled hallways, and the clothes shooter Adam Lanza wore. The report also includes dashcam video from police officers speeding to the scene, nearly three hours of audio files and more than four hours of heavily redacted video shot by investigators inside the school and the Lanza home. State law prevents the release of crime scene photos that show the bodies of the victims.

The report quotes an unnamed witness who says that Lanza may have targeted the nearby school because his mother Nancy had once worked there.

A citation found in the Lanza home thanks Nancy Lanza for her volunteer service at the school, which Adam attended, in 1999. "Dear Mrs. Lanza, Thank you for being such a special volunteer. The children achieved a most successful year with the dedication from your active involvement."

It also quotes a witness whose name is redacted that Adam had a grudge against the school. “Lanza hated his mother and Sandy Hook,” said the unnamed witness, “because his mother worked there. Lanza apparently felt that his mother loved the students more than him.”

The Connecticut State Police have released a more than 7000-page report detailing their investigation into the Sandy Hook Elementary School shooting – many of the documents are heavily redacted. NBC's Natalie Morales reports

A male friend told investigators that Nancy Lanza wanted to sell her home and move to North Carolina or Washington state. In North Carolina, she reportedly said, she had a friend who had a computer business and could train Adam. In Washington, she knew of a special school that could educate him.

The report makes no conclusions about a possible motive. A summary report released in November said that Lanza had no clear motive, but was obsessed with school shootings -- particularly the Columbine massacre of 1999 -- and planned both the Sandy Hook rampage and “the taking of his own life.”

The new report also says that a police officer who attempted to rescue a teacher and children hiding in a bathroom had to convince them he was really there to help. When he identified himself as a police officer, the teacher said, “You’re not the police, I don’t believe you” until a trooper began removing kids from the room.

Lanza, 20, killed his mother at the Newtown, Conn. home they shared and then drove to the nearby elementary school, where he murdered 20 children and six staffers with a Bushmaster rifle before taking his own life.

Slideshow: Newtown school massacre Jessica Hill / AP A nation mourns after the second deadliest school shooting in U.S. history at Sandy Hook Elementary, which left 20 children and six staff members dead. Launch slideshow

The release of the full police report, according to the state’s Department of Emergency Public Services and Protection, “is indicative that this State Police criminal investigation is concluded.”

“I hope that the release of this report, though painful, will allow those who have been affected by it to continue in their personal process of healing, and will provide helpful information that can be put to use to prevent such tragedies in the future,” wrote DESPP Commissioner Reuben Bradford in a letter accompanying the report.

The release comes more than a month after the Danbury State’s Attorney’s office published a long-awaited summary report based on the state police investigation.

The original 48-page summary report said that there was "no clear indication" why Lanza chose Sandy Hook for the shooting, other than that it was close to his home. The report said Lanza had a strained relationship with his mother Nancy, telling a witness he would not feel bad if something happened to her.

Investigators said Lanza had a spreadsheet that listed famous mass killings, and had posted on an "internet blog" that "focused on mass shootings and in particular the Columbine shootings." The report's appendix noted that a computer hard drive included a computer game called "School Shooting," in which the player controls a character who enters a school and shoots students.

Lanza, whose bedroom windows were covered with trash bags, had also downloaded videos about Columbine shooters Eric Harris and Dylan Klebold, surveillance footage of a Cleveland school shooting, video of a mall shooting and two videos of suicide by gunshot.

At age 10, according to the report, Lanza helped write a book that includes characters who kill children, carry bags full of guns and say they enjoy hurting people, “especially children.” The “Big Book of Granny” was apparently written as part of a fifth-grade class assignment.

Police, according to the report, arrived at the school "within minutes of the first shots being fired. They went into the school to save those inside with the knowledge that someone might be waiting to take their lives."

According to the report, Lanza refused to take suggested medication and didn't engage in recommended behavior therapy. Investigators found no medication in his system "that would affect his behavior."

Lanza's mother Nancy consistently described him as having Asperger's Syndrome, said the report. She said he was unable to make eye contact, was sensitive to light and didn't like to be touched. She said there were marked changes in his behavior around the seventh grade, when he became more withdrawn.

Nancy Lanza "took care of all the shooter's needs,” according to the report. A witness, however, told investigators that Lanza "did not have an emotional connection" with her. "A person who knew the shooter in 2011 and 2012 said the shooter described his relationship with his mother as strained," said the report.

In November 2012, just a month before the shooting, Nancy was concerned about Adam because "he hadn't gone anywhere in three months," said the report, "and would only communicate with her by email, though they were living in the same house." Nancy Lanza, however, never expressed fear for herself or anyone else at the hands of her son.

Nancy Lanza wanted to buy the shooter a new pistol for Christmas, according to the report, and "had prepared a check for that purpose to give the shooter."

The long-awaited summary of the second-deadliest mass shooting in U.S. history omitted much information from the investigative file, including transcripts of 911 calls, some witness statements from children and most crime scene photos.

State’s Attorney Stephen Sedensky and the town of Newtown went to court to try and prevent the release of 911 calls from the school or transcripts of them, arguing that making them public could jeopardize the investigation. Tapes of seven calls were ultimately made public on Dec. 4.

Other evidence from the state's investigation may never be made available to the public.

A Connecticut law passed earlier this year in response to the shooting prohibits the release of photographs, film, video and other visual images showing a homicide victim if they can "reasonably be expected to constitute an unwarranted invasion of personal privacy of the victim or the victim's surviving family members."

More from NBC News Investigations:

Follow NBC News Investigations on Twitter and Facebook