An exhaustive report into last year's shooting in Newtown, Conn., has found no clear reason why 20-year-old Adam Lanza killed 20 first graders, six adults, his own mother, and ultimately himself. According to a 48-page summary released Monday, state investigators determined that Lanza acted alone and that no charges will be made in the case, but could only point to a history of mental-health issues, "a strong interest in firearms," and "a preoccupation with mass shootings" as possible motives.