Prosecuting attorneys in Connecticut have concluded that 20-year-old Adam Lanza "displayed no aggressive or threatening tendencies" before he massacred 20 children and six adults at the Sandy Hook Elementary School in Newtown about a year ago.
Thousands of pages of documents involved in an investigation into Lanza were released recently. They, along with a new book - "Newtown, an American Tragedy" - show Lanza was, indeed, deeply disturbed. The book's author, Matthew Lysiak, notes several people acquainted with Lanza worried about him.
But no one recognized Lanza was a mass murderer in the making.
He was obsessed with violent video games and real firearms. He was reclusive and studied mass murderers intensively.
That description could fit tens of thousands of people who would never harm another person, however.
If Americans are learning anything about the psychology of mass murder, it is that we know next to nothing that is of practical help.
The danger in blaming, say, violent video games or access to firearms is that it will distract us from learning what really goes wrong in the minds of spree killers. Until we adopt a laser-like focus on the mental health question, there will be more horrifying scenes like that in Newtown.