In a story that serves as a sad metaphor for much of the violence that plagues kids in urban America, Boston police easily identified the two teen killers of a teen victim. “The challenge was how to safely bring in the very young suspects — one of them just 14 — and to arrest them without risking harm to the boys or to officers or triggering further violence in an already fraught neighborhood. So police turned to the boys’ mothers, and their mothers turned them in.”