morf13 wrote:...then why is it a stretch to accept the desktop poem as his writing too?
For me it has everything to do with the nature of that poem. It reads like a suicide fantasy (for lack of a more precise term) to me. It reads like something a regular student, most likely female, would have written. It doesn't smack of Zodiac or any other killer whatsoever to me. That's the stumbling block. Now, if you could show me Z's fingerprints on that desktop – or a unique phrase of some sort, or a signature that can't be mistaken – then I have to hold my hands up and say: Alright, so he actually wrote this poem, for who knows what reason, in spite of it looking like it was written by a young, non-murderous woman. But we don't have anything like that.
Some guy discovers a poem he considers morbid, no doubt with the Bates murder still fresh in his mind. He tells the police about it (or his supervisors or whatever, who then inform the police). The police conclude it is morbid too. And tell other departments about it – and then a certain reporter. And then, eventually, the SFPD make sure the morbid poem is photographed – and then our friend Morrill looks at said photograph and says...what? We don't know that, in detail, but what he says confirms what the SFPD want confirmed, because at this point they have embraced the Riverside connection as a whole, they believe that Zodiac is connected to Riverside, that he killed Bates and that he wrote the Confession and the notes: Morrill confirms all this, apparently down to the capital letters on the Confession envelope. But unlike the Confession and the notes, the desktop isn't undoubtedly connected to the Bates case. And the only formal or professional connection is Sherwood Morrill's opinion: No fingerprints, no DNA, no explicit references, no undeniable signature or unique phrases. Just the opinion of a handwriting expert.
Good enough for some, certainly good enough for the SFPD (but seemingly not for other departments) at the time. Personally, I say give me something solid. Until then, it's not confirmed as far as I'm concerned – and as such no theory should rely on it being Z's work. That's the principle I'm working from, others will no doubt disagree and that's more than fine. Some very clever people think it's Zodiac – they could very well be right.