Central to Crossan's methodology is the dating of texts. This is laid out more or less fully in "The Historical Jesus" in one of the appendices. He dates part of the Coptic "Gospel of Thomas" to the 50s CE, as well as the first layer of the hypothetical "Q Document" (in this he is heavily dependent on the work of John Kloppenborg). He also assigns a portion of the "Gospel of Peter," which he calls the "Cross Gospel", to a date preceding the synoptic gospels, the reasoning of which is laid out more fully in "The Cross that Spoke: The Origin of the Passion Narratives". He believes the "Cross Gospel" was the forerunner to the passion narratives in the canonical gospels. He does not date the synoptics until the mid to late 70s CE, starting with the Gospel of Mark and ending with Luke in the 90s. As for the Gospel of John, he believes part was constructed at the beginning, and another part closer to the middle, of the 2nd century CE. Following Rudolf Bultmann, he believes there is an earlier "Signs Source" for John as well. His dating methods and conclusions are quite controversial, particularly regarding the dating of Thomas and the "Cross Gospel".