"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," the prosecutor's report added.
In Friday's report, police quoted an unidentified man who said he had dated Nancy Lanza in 2011 and remained friends with her. The man said she told him "she did not want to be in Connecticut the week of the shooting and was considering taking a trip to be sure she was out of town. This was thought to be some sort of foreshadowing of the incident," the report said.
The London trip was canceled, he said, because of "a couple of last minute problems on the home front," the report said. The unidentified man said he did not know what the problems were.
The man said "he knew Lanza to own weapons and that she invited him to go shooting because it was a good stress release."
He told investigators that he visited her house only once and never met Adam. He said Nancy Lanza had retired from work because of her son's Asperger's syndrome. She wanted to be with her son, the man said.
Lanza had a strange relationship with his mother: They lived in the same house but communicated by e-mail, according to the prosecutor's report last month. He refused to touch doorknobs and changed clothes several times a day. He loathed holidays and birthdays.
Lanza and his mother frequently went target shooting together. Friday's report said "a stand alone metal gun safe was located in the closet" in the Lanza home. "The door of the safe was found open. The door and the lock did not appear damaged."
Adam Lanza's relationship with his father was equally strange. Peter Lanza told investigators that he would reach out to Adam via e-mail six to eight times a year, even though Adam stopped responding altogether sometime in 2010, the report said.
"Peter stated that when Adam was approximately 8-9 years old he told him that 'he loved being a kid,'" said the report. "Peter also stated that Adam enjoyed his time at the Sandy Hook Elementary School when he was a student there."
Peter Lanza said that when his son was 11 or 12 years old, his demeanor changed, and he became more stressed and frustrated. And the father said he did not have a lot of interaction with his son during the year preceding the shooting, with Peter Lanza feeling "his ex-wife Nancy was a contributing factor to Adam distancing himself from him."
An unnamed man who said he spoke to Nancy Lanza in the days before the massacre told investigators that she was planning to sell her house and move to Washington state or North Carolina. In Washington, the report said, Adam was to attend a special school he wanted to go to. If they went to North Carolina, Adam was to work for a friend of Nancy Lanza who owned a computer technology business.