Both Burkett & Dan Rather are residents of Texas so that is why the Texas Penal Code is applicable, and while I doubt that it can be proved that Rather knowingly was in on the forgery, Burkett has admitted that he "deliberately misled" CBS news producer Mary Mapes.
If Burkett didn't forge the documents, then he knows who did, and the above penal code can be brought on him to give his source, and then upon the source itself.