Adam Lanza was a strange young man in many ways, those who knew him say. But there were no hints he would turn violent, as he did last Friday when he murdered his mother, then massacred 20 children and six adults at an elementary school in Newtown, Conn.
Lanza displayed some troubling traits, to be sure. He was a loner, very selfish and apparently not given to displaying his emotions, according to one educator who knew him as a high school student. But that man added he would never have expected Lanza to have become a mass murderer.
Even as Americans mourn for those killed by Lanza, we once again search for ways to prevent horror such as that he unleashed. To some, the key to preventing these attacks is recognizing those prone to murderous attacks.
But mass killers - and there have been many in this country alone - have been studied intensively by psychologists and others attempting to identify environmental and behavioral factors that link them, to learn what makes them turn violent.
Without exception, serious researchers learn it is difficult to do so. Thousands of people may suffer from a variety of similar mental or emotional disorders but never act out violently.
What researchers do learn is that the killers' behavior in days and weeks leading up to their violent sprees sometimes provides hints concerning what is to come.
Clearly, more investigation - much more - on the subject is needed. Identifying murderous minds such as Lanza's should be a priority for researchers.