I think it's worth stating here pretty pointedly that despite what some comments below speculate about the killer's supposed low intelligence based on grammatic

I think it's worth stating here pretty pointedly that despite what some comments below speculate about the killer's supposed low intelligence based on grammatical and spelling errors in the text of his messages, I very much doubt that anyone without a fairly strong level of cognitive capacity could have or even would have created such fairly complex ciphers (and without the aid of more widespread computing or knowledge of crypto as is the case today).