Given a chance to review the long-awaited investigative report on last December’s Newtown Elementary school shooting, Connecticut lawyers said they were confronted with shocking details of Adam Lanza’s final days.

The report for the first time described Lanza’s bedroom in the home he shared with his mother on Yogananda Street. The windows were covered with black trash bags. In the home, investigators found information Lanza had collected about gun violence, including spreadsheets he created to document mass shootings.

The report released by the state’s attorney in Danbury, Stephen Sedensky III also provided the most comprehensive timeline of Lanza’s rampage Dec. 14, which started when he fatally shot his mother at their home and then went to the elementary school, arriving at 9:30 a.m. In less than 11 minutes, he killed 20 first-graders and six adults, before turning the gun on himself.

“The report appropriately focuses on the actions and background of the shooter,” said Morgan Rueckert, a Shipman & Goodwin attorney in Harford who is representing 22 of the Sandy Hook victims’ families. “The attached timeline also goes into great detail about the content of 911 calls as well as the precise timing of events.”

The report also painted a picture of a troubled young man.

“The purpose of the investigation was to determine what crimes had been committed and whether anyone will be prosecuted as a result of those crimes. Based on a painstaking investigation it is determined that there will be no arrests or prosecutions. The Connecticut State Police are to be commended for their tireless work on this investigation and their consideration of the families and victims involved,” said the report’s author, Sedensky.

But Sedensky said despite the depth of the investigation, there is one question that might never be answered.

“The obvious question that remains is: ‘Why did the shooter murder twenty-seven people, including twenty children?’” Sedensky’s report stated. “Unfortunately, that question may never be answered conclusively, despite the collection of extensive background information on the shooter through a multitude of interviews and other sources. 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, however, did reveal evidence of Lanza’s mental health problems. “What we do know is that the shooter had significant mental health issues that, while not affecting the criminality of the shooter’s mental state for the crimes or his criminal responsibility for them, did affect his ability to live a normal life and interact with others,” Sedensky said.

John Thomas, professor at Quinnipiac University Schools of Law & Medicine, said what was most startling about the information provided about Lanza’s were the signs that he planned the rampage.

“What the summary report conveys most powerfully is the depth of Adam Lanza’s obsession with carrying out the Sandy Hook massacre. Lanza had collected photocopies of news stories of the shooting of school children back as far as an 1891 shooting in New York, with an emphasis on reports about the 1999 Columbine shooting,” Thomas said. “He had prepared a spreadsheet of all school shootings in the country, entering the date, location, and other salient facts. GPS data in his car revealed that Lanza had scoped out the Sandy Hook Elementary School the day before carrying out the tragic events of December 14, 2012.

The report also paints a disturbing picture of Lanza’s struggle with mental health issues beginning in preschool and slowly worsening through the years, culminating with his withdrawal from society and fixation on committing last year’s horrific act.

Investigators recovered violent video games, violent videos of shooting events and photos of Lanza holding a gun to his head, but they acknowledged that a sizeable amount of information would not be revealed because Lanza had destroyed his computer.

Based on interviews with people who knew Lanza, the report said, “those who knew the shooter describe him in contradictory ways. He was undoubtedly afflicted with mental health problems; yet despite a facination with mass shootings and firearms, he displayed no aggressive or threating tendencies.”

The report indicates that nearly six minutes passed between the arrival of the first Newtown police officer and the time local officers entered the school. A timeline released with the report says the first officer arrived behind the school at 9:39 a.m. after the shooting was reported. Two other Newtown officers then arrived at the school, and gunshots were heard in the background.

The last gunshot officers heard, which is believed to be the suicide shot by Adam Lanza, was heard at three seconds past 9:40.

The report says Newtown officers entered the school at 47 seconds past 9:44.

Joel Faxon, an attorney at Stratton Faxon in New Haven and member of Newtown’s police commission, said commission members will review the report, including the amount of time it took for police to enter the school. But, he noted, that decision has to be put in the context of the entire crime scene.

“There were a lot of things going on outside the school a the time, there were shots being fired inside and when [officers] got there, there were people outside,” Faxon said. “It was an ongoing, stressful, developing crime scene, and at the same time, we need to know exactly what happened during that period of time [before police entered the building].”

Faxon said that in reviewing the investigative report, he learned a lot about Adam Lanza’s mental state. Specifically, the report referred to the shooter’s windows being covered with black plastic, and violent images of school shootings and suicides were found in his room.

“The material I hadn’t been made aware of in the past really focused on Lanza’s complete disconnect from reality,” Faxon said. “I know the guy was crazy, but I had no idea that it was as bad as depicted in the report. And how his mother would provide him with checks for him to get weapons and allowing him to live in her house in the mental state he was in. They would only communicate though emails and they lived together in the same house.”

If Lanza’s mother, Nancy, hadn’t been the shooter’s first victim, Faxon said he believes she would have been criminally responsible for providing him with the weapons “in his mental state.”

“To live with a person who, to me, seems obviously insane is really shocking. How she could have all of those weapons in that house is beyond me.”

There had been some criticism from public officials and open records advocates about the length of time it was taking Sedensky to release the results of the state investigation. In fact, the 44 pages released Monday represent only a fraction of the information gathered by investigators. A full report is scheduled to be released early next year.

“A release of a summary report before the release of the full report is highly unusual,” said John Thomas, a professor at Quinnipiac University Schools of Law & Medicine, who studies issues surrounding mental health and gun laws.

Dan Klau, a Hartford attorney who specializes in First Amendment law, agreed that the decision to release a summary report before the full evidence file is a reversal of standard practice.

“What I found troubling about the approach of the state’s attorney is that from my perspective, he seems to have forgotten his job is to represent the state of Connecticut,” said Klau, who practices at McElroy, Deutsch, Mulvaney & Carpenter. “His conduct in many instances has seemed more akin to an attorney in private practice representing Sandy Hook families. What I found troubling about the approach of the state’s attorney is that from my perspective, he seems to have forgotten his job is to represent the state of Connecticut.”

Rueckert, who is representing victims’ families, said it is important for the government to keep the victims in mind when releasing information.

“I think it’s appropriate under these circumstances to take a harder look now at what should be released and in what manner,” Rueckert said. “For those clamoring for the release of detailed information of the mechanism of how a heavily armed person smashed their way into an Elementary School and murdered 26 children and teachers — I must respond that there is no mystery there, schools are not fortresses, and why do you need to know who was shot when and how, what purpose is served other that satisfaction of morbid curiosity? The important question rather is about Adam Lanza, and how he had access to guns, and ammunition and how he was allowed to plan this and how his so very serious problems were not properly addressed.”

Gov. Dannel Malloy weighed in on the report shortly after its release.

“My thoughts today are with the people who lost a loved one at Sandy Hook Elementary School, as they have been nearly every day since the tragedy. The release of this report will no doubt be difficult on them. But if there is one thing that I believe we must do, it’s that we must honor the lives that were lost by taking steps to protect ourselves from another horror like this. I hope that the information in this summary and in the supporting documents that will be released by the State Police takes us closer to that goal.”