Absence of actual authority–John Yoo had no authority to issue an opinion binding OLC, so Yoo Two was invalid from the moment it was issued. Similarly, Bradbury is not in fact the head of the office of OLC, and is not authorized to prepare or deliver opinions with the authority of the attorney general. His opinions are the opinions of a lawyer named Steven Bradbury, they are not the opinions of the Attorney General which have special force under the Judiciary Act of 1789.
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Of particular importance, it notes that Yoo conferred with the Criminal Division (then headed by Michael Chertoff, assisted by the current head, Alice Fisher), with respect to the application of statutes prohibiting torture against military actors. In testimony before Congress, Chertoff repeatedly denied involvement in the preparation of the torture memoranda, notwithstanding mounting evidence to the contrary. The candor of his testimony, and that of his successor Alice Fisher, has repeatedly been challenged by others who were involved at the time.
http://harpers.org/archive/2008/04/hbc-90002785