NSA's United States Signals Intelligence Directive 18 (USSID 18) strictly prohibits the interception or collection of information about "..US persons, entities, corporations or organizations..." without explicit written legal permission from the Attorney General of the United States. The Supreme Court has ruled that intelligence agencies cannot conduct surveillance against American citizens.Therefore, if Clarke determined that the AD operation was essentially spying on U.S. citizens, as the articles pertaining to this operation have suggested, he would have been the one to order the papers destroyed.
"My money is on Richard Clarke..."
In other words...pure speculation.