We don't know anything about the situation. Ritual sacrifices I don't believe either but it might be so that a real, very obvious, motive, existed. It is impossible to sort out amidst all barrage of news, what is a rumor, and what, truth. So, ritual sacrifices I don't believe, but what if girls were making photos of some rituals and made these guys angry? You mentioned meth. It seems to be a strong component for everything.
In short, I don't specifically believe it was some group because I believe it was personal. But since the whole case did not become clear after six years of investigation, and mostly! - a young man with curly hair and a Teutonic chin, whose sketch DC unveiled at 2019 conference, has nothing to do with RA, nothing makes sense.