Everyone remember "Tyger Tyger"? The poem that Red John recited? Well, the author of that poem is William Blake (often connected with Serial kiillers because of his dark christian-based work).  Well, Blake is quoted by another character, once, in the entire series, at the end of a case, NOT in the presence of Jane. Blake was quoted by Bertram, and Cho picked up on the fact that the author was Blake, and then this was NEVER mentioned again. A perfect piece of dramatic irony, a clue that would give Jane everything he needs to know, but Cho didn't know to give it to him.