What's sinister is the way Bugliosi misrepresents the details in order to fit his preferred narrative.
But Givens was interviewed several times by the FBI and the Secret Service between November and April. It wasn't until April that the story about going back for his cigarettes and seeing Oswald first popped up. And that was after Revill told Gemberling that Givens had been previously handled by the Special Services Bureau on a marijuana charge and he believes that Givens would change his story for money.