From my Copyright text, a little jab at California:
"The facts of the Oliver case are odd, even for California. The defendant was permitted to appropriate material from a copyrighted work because it had been represented by the plaintiff as the revelations of a deceased entity from another world." (41 F.Supp. 296).
You can't copyright facts or historical interpretations. Apparently because this was presented as factual material, it couldn't be copyrighted. You can't claim authorship in material represented as fact, even if a reasonable person wouldn't believe it.