In his kind of autobiography (really a book by Nuel Emmons that is based on notes from conversations with Manson from prison (that I read as a teenager, so my memory is hazy to say the least)) Manson himself sort of verifies the drug theory. He makes the claim in that book that another one of his family killed another drug dealer up in the Bay Area, and in the course of that murder the dude (whose name escapes me) did a bunch of writing in blood ("PIG", etc). Those details were never released in the press, so when they did the next murders (for ambiguous reasons that are never really fleshed out) they recreated some details in order to make the cops think that they had the wrong guy for the Bay Area murder. According to Manson, the cops in LA apparently never spoke to the Oakland or SF cops, and not a second thought was given to the serial killer ruse. Just an interesting aside.