Al Qaeda operates by launching surprise attacks on civilian targets with the goal of massive casualties. Our only means for preventing future attacks, which could use WMDs, is by acquiring information that allows for pre-emptive action.

He has written two books on presidential power and the war on terrorism and many articles in scholarly journals and newspapers. In international law Yoo has written that the rules governing the use of force must be understood to allow nations to engage in armed intervention to end humanitarian disasters rebuild failed states and stop terrorism and the proliferation of weapons of mass destruction.  
War by Other Means: An Insider's Account of the War on Terror.

In 2009 two days after taking office President Barack Obama in Executive Order 13491 repudiated and revoked all legal guidance on interrogation authored by Yoo and his successors in the Office of Legal Counsel between September 11 2011 and January 20 2009. John Choon Yoo (born July 10 1967) is an American attorney law professor and author.