(CNN) — Connecticut authorities closed the book on last December’s massacre at Sandy Hook Elementary School on Monday without answering what drove the 20-year-old behind the rampage.
A 44-page summary of the second-deadliest shooting in U.S. history outlines how gunman Adam Lanza killed his mother, then stormed the elementary school and killed himself as police arrived. But investigators haven’t determined a motive for the assault, which left 20 first-graders and six adults at the grade school dead in less than 11 minutes.
“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,” Monday’s report states.
Lanza “had significant mental health issues that affected his ability to live a normal life and to interact with others,” the report states. But it adds, “What contribution this made to the shootings, if any, is unknown as those mental health professionals who saw him did not see anything that would have predicted his future behavior.”
There were no drugs in his system at the time of the killings, according to autopsy results included in the report. Lanza “did not drink alcohol, take drugs, prescription or otherwise, and hated the thought of doing any of those things,” investigators found.
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“With the issuance of this report, the investigation is closed,” Monday’s report concludes.
The killings in Newtown, about 80 miles outside New York, happened less than five months after a similar bloodbath at a movie theater in Aurora, Colorado, outside Denver. The killings ignited a nationwide debate over gun violence, school safety and mental health.
Lanza had “an obsession” with mass murder and “a strong interest in firearms,” the report states. On his computer, investigators found a spreadsheet detailing mass murders over the years, two videos depicting gunshot suicides, two pictures of Lanza pointing guns at his own head, and movies and a video game depicting school shootings.
But violent video games weren’t his only pastime: He also was obsessed with the dancing game “Dance Dance Revolution.” He not only played it at home, he went to a local theater that had a version in its lobby nearly every weekend, playing it for as long as 10 hours at a time.
Another hard drive found in his home appeared to have been intentionally damaged, and investigators were unable to recover anything from the device.
And investigators found “a large number” of guns in the home. All of them had been bought by his mother, Nancy Lanza, who grew up with firearms and “thought it was good to learn responsibility for guns,” the report states. Both she and Adam Lanza shot pistols at a local range, where Adam “was described as quiet and polite.”
Nancy Lanza, 52, “took care of all of the shooter’s needs” and “worried about what would happen to the shooter if anything happened to her,” according to the report.
“The shooter was particular about the food that he ate and its arrangement on a plate in relation to other foods on the plate,” it recounts. “Certain types of dishware could not be used for particular foods. The mother would shop for him and cook to the shooter’s specifications, though sometimes he would cook for himself.”
Nancy Lanza did her son’s laundry every day, but was not allowed into his room — “No one was allowed in his room,” where the windows were covered with black plastic trash bags, the report notes. Adam Lanza “disliked birthdays, Christmas and holidays,” forbidding his mother from putting up a Christmas tree: “The mother explained it by saying that shooter had no emotions or feelings.”
One person described Lanza’s relationship with his mother as “strained,” while another told investigators he didn’t appear to have “an emotional connection to his mother.” But others said Nancy Lanza “was the only person to whom the shooter would talk.
The morning of the massacre, Lanza shot his mother several times in the dead with a .22-caliber rifle while she lay in bed, the report states. He then headed to Sandy Hook, where he had attended grade school — but “as best as can be determined, the shooter had no prior contact with anyone in the school that day.”
Four guns and more than 300 rounds of ammunition were found with Lanza, including the .223-caliber Bushmaster semi-automatic rifle used at the school and the 10mm Glock pistol he used to kill himself. Another pistol and a shotgun weren’t used, the report states.
Monday’s report is separate from a much longer evidence file that Connecticut State Police will release at an unspecified date. The family of Victoria Soto, a teacher who shielded her students before being shot to death, said the release is “yet another blow that our family has been dealt.”
A statement from the family said, “While others search for the answer as to why this happened, we search for the how. How can we live without Vicki? How do we celebrate Christmas without Vicki? How do we go on every day missing a piece of our family? Those are the questions we seek the answers for. There is nothing in the report that will answer those for us.”
Connecticut Gov. Dannel Malloy said the report’s release “will no doubt be difficult” for the relatives of those killed at Sandy Hook.
“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,” Malloy said. “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.”
Victims’ family members were informed of the report, said Mark Dupuis, a spokesman for Danbury State’s Attorney Stephen Sedensky, whose office conducted the investigation.
Dupuis declined to provide details about when, where, and how the families were given the details of the report.
“We are sensitive to the needs of the families, and those needs are being addressed,” Dupuis said.
After the Newtown killings, a handful of states — Connecticut among them — passed new regulations on background check limits, magazine capacity and types of firearms legally available. But efforts to pass even limited legislation at the federal level were thwarted by a Republican filibuster in the Senate; the Obama administration then announced limited executive reforms in place of tougher laws.