NEW YORK — It’s been almost one year since a gunman massacred 20 children and six adults at Sandy Hook Elementary School in Newtown, Conn. This week, investigators have released chilling details about the case, which include disturbing findings on Adam Lanza, the man responsible for the murder spree.

Lanza was apparently obsessed with mass murders and mentally twisted to the point that his mother planned to move him out of state so he could attend a special school. Despite this, she had him living in a home with firearms and ammunition and gave him money to buy a gun for Christmas.

The information was released Monday, November 25, is the most detailed account yet of the Dec. 14, 2012.

Among other things, it said Lanza, 20, kept a spreadsheet of mass murders, hated to be touched, and did not allow anyone — including his mother, Nancy Lanza — into his bedroom. He covered his bedroom windows with black trash bags, disliked birthdays and holidays, would not let his mother put up a Christmas tree, and made her get rid of a cat because he didn’t want it in the house.

As time went by, he only spoke to his mother via email, even though they lived together.

But the 48-page report, a summary of the police investigation that includes 78 photographs of the school and the Lanza home, does not offer a reason for Lanza’s rampage or his decision to target the school.

“The obvious question that remains is: Why did the shooter murder 26 people, including 20 children? Unfortunately that question may never be answered,” it said.

The report provided a detailed timeline of the events that Friday morning, based on interviews with witnesses, including children who survived.

It delved into Lanza’s childhood and mental problems and noted that nobody considered him a threat. Despite his odd behavior. Toxicology reports showed no sign of prescription medication or any other drugs or alcohol in Lanza’s system at the time of the shooting.

According to police, Lanza shot his mother sometime between 8 and 9 a.m., using a .22-caliber rifle. Someone living near the Lanzas’ home in a hilly, upscale neighborhood reported hearing “two or three” gunshots during that time.

Then Lanza got into his car and drove a few miles to the school. He parked outside the low-slung building and approached the front entrance armed with a Bushmaster rifle, a Glock 10-millimeter pistol, a Sig Sauer 9-millimeter pistol and a “large supply of ammunition,” according to the report. The doors were locked because classes had begun, so Lanza shot open the plate-glass window on the door leading into the lobby.

Wearing a hat, sunglasses, yellow earplugs and black fingerless gloves, he began strolling down the hallway. “The shooter walked normally, did not say anything, and appeared to be breathing normally,” the report said.

Lanza’s first victims were principal Dawn Hochsprung and school psychologist Mary Sherlach, who were in Room 9 when they heard glass shattering and “loud banging.” They went into the hallway and quickly were shot to death, but not before Hochsprung warned a third staffer behind her, “Stay put!”

That staffer was also shot but survived. She crawled back into Room 9 and dialed 911.

By now, other staff members had taken shelter in the school’s main office. Lanza was heading toward classrooms 8 and 10, where he killed 20 children and four adults.

As the gunfire raged, staff and students hid wherever they happened to be. The staff used various ways to keep the children calm, reading to them or having them color or draw pictures.

The first 911 call was made about 9:35 a.m. Less than four minutes later, the first police arrived at the school, according to the report. Less than five minutes after that call, Lanza shot himself.

“In fewer than 11 minutes, 20 first-grade pupils and six adults had lost their lives,” the report said. It noted that all the weapons found in Lanza’s home or with him at the school had been legally purchased by his mother.

Nancy Lanza, who was divorced from Adam’s father, “took care of all the shooter’s needs,” according to the report, and indicated that she didn’t work because of his condition. Nonetheless, she allowed Adam easy access to firearms, and one of the items found in their home was a check, written by Nancy Lanza to Adam and dated “Christmas Day,” with a notation that it was for him to buy himself a CZ 83 pistol.