Leilani asks whether she needs a contract with the authors of a news article and a book about true people and events that occurred over half a century ago before she can market a screenplay about those people and events.
This video provides my answer:
First off, this isn't a copyright “public domain” issue, sice facts aren't protected by copyright. Instead, we look to the Right of Publicity, which governs a person's right to control commercial uses of his or her name, likeness, or persona. But even where, as here, the first amendment's protections are strong, most entertainment lawyers will recommend having a deal in place to secure the subjects' cooperation, and promise not to sue.
The best advice in these situations is to consult with an experienced, knowledgeable, and well-connected entertainment lawyer, about the specifics in each situation.