HARTFORD, Conn. (AP) — Why Adam Lanza went on his murderous shooting rampage at a Newtown elementary school is a mystery and may never be known, prosecutors said in a report Monday as they closed their yearlong investigation.
Lanza, 20, was obsessed with mass murders and the 1999 Columbine High School shooting in particular, but wasn't aggressive or threatening before the attack, according to the summary by the lead investigator, State's Attorney Stephen Sedensky III.
The report describes a gunman who had "significant mental health issues" but had sure knowledge of what he was planning: He had materials on mass murder, he smashed his computer hard drive, and he used earplugs during the shooting.
Lanza killed 20 first-graders and six educators with a semi-automatic rifle inside Sandy Hook Elementary School on Dec. 14. He also shot his mother to death inside their home before driving to the school, and committed suicide with a handgun as police arrived.
"The obvious question that remains is: 'Why did the shooter murder 27 people, including 20 children?' Unfortunately, that question may never be answered conclusively," the report said.
Lanza "was under no extreme emotional disturbance for which there was a reasonable explanation or excuse."
Sedensky also said there was no clear indication why Lanza chose Sandy Hook Elementary other than that it was close to his home.
The report said noted that in 2005, he was diagnosed with Asperger's disorder and lacked empathy for others. But "what contribution this made to the shootings, if any, is unknown."
Asperger's is an autism-like disorder that is not associated with violence.
Lanza might have hinted at his intentions online in the days before the massacre, the report indicated.
A Texas woman contacted Hartford police the day of the Dec. 14 attack to say her son had interacted with someone while playing a videogame 20 hours earlier who said there would be a school shooting, according to the report. It wasn't clear from the report whether she contacted authorities before or after the massacre.