A loving mother. A teenage killer. "Plenty of lurid details and twists and turns . . . A story about the consequences of an overwhelmed justice system" ( West End Word).   On a crisp December day in 1963, Nancy Zanone left her young son and daughter playing in the backyard while she went inside to check the laundry. She never came back. A troubled teen prowling for unlocked doors along Chippewa in South St. Louis surprised her in the kitchen and stabbed her to death. Despite Joseph Arbeiter's confession and hard evidence, he was freed on a technicality. In response, Zanone's family fought to change how juvenile murderers are tried in the state of Missouri. Local authors Vicki Berger Erwin and Bryan Erwin investigate the senseless tragedy and the family's quest for justice.   Includes photos