It was my understanding that Manson claimed to be the leader or a high-ranking member of a scientology splinter group as well, The Process Church (”Ultimate Evil”, Terry Maury, and “Helter Skelter”, Vincent Bugliosi).
I remember asking a CoS auditor about The Process and he knew nothing about it but warned me against having anyone audit me but someone qualified to do it. That’s the one time I agreed with the CoS entirely. ;)
He may well have been. I have no idea.
I've got no love for the 'church', but I won't try to pin Charles Manson on them. Lots of well known people have been passing members of that organization, including John Brodie, Stanley Clarke, Ingo Swan, Christopher Reeve, Chaka Khan, and many others.