Bon tells them

In the mix-sixties, while in McNeil Island Prison in Washington State, Charlie (Manson) picked the brains of a Scientologist inmate, at the same time he studied Masonic ritual and absorbed an indiscriminate amount of occult lore; it may have been then that he read Stranger in a Strange Land, and it was certainly then that he developed a kind of persuasive charisma based on (Scientologist) Hubbard's auditing.