TAMPA, Fla. (AP) — For nearly half her life, Ruby Williams has prayed for her daughter, Brenda: "Lord, let her be alive."

She's repeated this prayer tens of thousands of times, starting in the mid-1970s, when she lived in a four-bedroom apartment with her husband and 12 children. Now 89 and a widow, she prays in a modest home near downtown Tampa, where she lives with two of her children.

Brenda, Williams' third child, has been missing since 1978. Since then, her family has subsisted on slender threads of hope: Maybe Brenda just walked away. Maybe she was living a new life, with a different fam...