The alleged spree killer who fatally stabbed three people in Manhattan told cops in a chilling confession that he targeted his innocent victims because they were “alone” and “distracted,” law-enforcement sources revealed Tuesday. The revelation about the purported cold-blooded admission by Ramon Rivera, 51, came shortly before he shuffled into Manhattan Criminal Court for his arraignment on three counts of first-degree serial murder. The bearded, raggedy Rivera sat stone-faced as Assistant District Attorney Megan Joy recounted how he allegedly attacked three times — and “with no provocation” — in an hours-long frenzy Monday morning that stretched from the West Side...