What is in the mind of a person who commits an act of mass violence? Are there warning signs the rest of us can detect?
Madeleine speaks with UCLA Psychologist Stephen Diamond, who has studied these questions for decades. Dr. Diamond has written several books on the subject. Diamond also writes a blog called "Evil Deeds" in Psychology Today.
Home Page Photo: A message is left on a highway overpass in remembrance of those killed down the street from the Sandy Hook School in Newtown, Connecticut. (Credit: Spencer Platt/Getty Images)