Burkett is the most plausible originator of the documents based on.
"..But also on Tuesday, Salon reported on a 2,600-word letter that Mr. Burkett had written to CBS, in which the former National Guardsman seemed to agree with the panel: He blamed CBS for failing to properly vet the documents, which he said he had offered only on the condition that he not have to explain their chain of custody.."
And:
The incredible clumsy nature of the fabrication which leads to the probablity they were the product of a demented amatuer.
And finally:
His incredible cock and bull story of how he got the documents, which understandably he was reluctant to disclose.