Reply #2: long article about legality here:

[steve2470]

The killing of bin Laden: Was it legal?

http://www.cnn.com/2011/WORLD/asiapcf/05/04/bin.laden.legal/?hpt=T1

(CNN) -- Was the killing of Osama bin Laden legal under international law?

The administration says yes, absolutely. Experts are unsure.

Attorney General Eric Holder told members of the Senate Judiciary Committee on Wednesday that the U.S. raid on bin Laden's compound was lawful "as an act of national self-defense."

Bin Laden "was the head of al Qaeda, an organization that had conducted the attacks of September the 11th," Holder said. "It's lawful to target an enemy commander in the field."

*much more at link above*