Complex sentence: Rankin later retracted the story, claiming it was a joke, but the rumor persisted, with a report in 2012 expanding on the rumor in "The Guardian", with speculation that Rowling's next book would be a crime novel.
Split into simpler sentences: Rankin later retracted the story, claiming it was a joke. The rumor persisted, with "The Guardian" speculating in 2012 that Rowling's next book would be a crime novel.