Dave Oranchak showed how a piece of text from a publication of Edward Hyde, Earl of Clarendon, fitted into the 408 cipher. In fact 46 consecutive characters were utilized. http://www.zodiackillerciphers.com/?p=144

Dave wrote "So, only one piece of text, from a vast collection of eleven billion pieces of text, fit into this chunk of cipher text. A one in eleven billion chance seems to suggest some significance. But don’t be fooled by this. Just because this rare event occurred, doesn’t mean it is anything more than a simple coincidence. If we didn’t already know the real solution to the 408, how do we know that this chunk of old and obscure text isn’t the correct solution?" When the rest of the 408 was decoded using Clarendon’s inserted text it was pure gibberish. Dave rightly stated that coincidences happen. But what I would like to know, bearing in mind the author of the 408 cipher may have had access to the Riverside library, is how many coincidences do we need before it’s not a coincidence anymore.

I looked at the preceding communication to the 408 cipher, that had any meaningful value. Therefore looked at the Riverside Desktop Poem. Its title was "sick of living/unwilling to die." So, I looked through more publications by Edward Hyde, Earl of Clarendon and found another of Edward Hyde’s quotes: “They who are most weary of life, and yet are most unwilling to die, are such who have lived to no purpose, — who have rather breathed than lived.” http://izquotes.com/quote/385232

For comparison "weary of life, unwilling to die" to "sick of living, unwilling to die." Although not identical, the Zodiac Killer may have gone on memory while titling the poem, and this reading material may have been available at the library. But the broader question is – how many coincidences eliminate doubt?

Edward Hyde, Earl of Clarendon was also an avid user of ciphers as revealed here in literary manuscripts;
"Naturally a substantial portion of Clarendon’s surviving manuscripts comprises his personal correspondence — both letters received by him from numerous correspondents and his own letters, written or signed by him, whether drafts, retained copies, or the letters actually sent. Among many notable examples are his letters written in August 1646 to William, Lord Widdrington, and to Sir John Berkeley, announcing the beginnings of his History of the Rebellion, and the letter he wrote on 12 November 1646, to Sir Edward Nicholas, describing his plan for the work and stating that he had already completed sixty sheets of it. Some of his letters, particularly those dating from the Civil War period, are wholly or partly in cipher or make use of pseudonyms in both salutations and signatures. The codes to sixteen such ciphers used by the Royalists are written out in Bodleian, MS Clarendon 94, and see also British Library,"

St Augustine of Hippo (13 November 354 – 28 August 430), was a Roman African, Christian theologian, whose writings influenced the development of Western Christianity and Western Philosophy. He wrote ""I do not know whether I would have been willing to die for him in the way that Orestes and Pylades, if the story is true, were willing to die together for each other. And yet a strange feeling had grown in me, and it was very different from theirs; I was sick and tired of living but I was too afraid to die." St Augustine of Hippo wrote the Confessions https://en.wikipedia.org/wiki/Confessions_(Augustine )