Since the death of Osama bin Laden Sunday, administration officials have repeatedly said that the mission to kill him complied with domestic and international law.
"Let me make something very clear," Attorney General Eric Holder told Congress on Wednesday, "the operation in which Osama bin Laden was killed was lawful. He was the head of al Qaeda, an organization that conducted the attacks of Sept. 11. He admitted his involvement."
But as new details of the operation emerge, and some Pakistani leaders protest the U.S. incursion into their state, legal experts say the administration must more forcefully lay out its case.
Law professor Kenneth Anderson, who specializes in legal issues related to war and terrorism, said that differing government accounts as to whether bin Laden was armed or invited to surrender or even involved in a firefight have muddled the legal debate and left the administration open to international criticism.
"Holder was not direct in stating that of course it was legal to target Osama bin Laden, legal to target with lethal force, legal to target without warning or invitation to surrender," said Anderson, who teaches at American University Washington College of Law. "And that has always been the U.S. legal position.
"The United States actually has firm legal views on these points, which unfortunately, probably for reasons of operational secrecy, the senior leadership hasn't properly communicated," he said.
To justify the use of force, the Obama administration relied on the Authorization to Use Military Force Act of Sept. 18, 2001, which allows the president to use "all necessary and appropriate force" against persons who authorized, planned or committed the 9/11 attacks, as well as international law derived from treaties and customary laws of war.
The Obama and Bush administrations have argued that the use of force is allowed under international law because of the continuing conflict with al Qaeda, and the need to protect the United States from additional attacks.
One year ago, in the midst of a debate about the legality of targeted killing of foreign nationals, Harold Koh, the legal adviser to the State Department, said in a speech that the administration's targeting practices complied "with all applicable law, including the laws of war."
"As recent events have shown," Koh said at the time, al Qaeda has not abandoned its intent to attack the United States, and so "the United States has the authority under international law, and the responsibility to its citizens, to use force, including lethal force, to defend itself, including by targeting persons such as high-level al Qaeda leaders who are planning attacks."
Koh conceded that because the conflict with al Qaeda does not involve conventional forces, the application of international law is "more difficult" and "more critical" for the protection of innocent lives.
But he assured that the administration had "carefully reviewed" the rules governing targeting operations to "ensure" that "only legitimate objectives are targeted and that collateral damage is kept to a minimum."
Koh's speech addressed whether a top al Qaeda official such as bin Laden could be targeted, but questions in the past few days have also centered on how bin Laden was killed.
"There's another issue being raised: Whether under the specific circumstances inside the compound, U.S. forces were justified legally in shooting him or instead should at that point have made a greater effort to take him alive," said Matthew Waxman, a professor Columbia Law School and an expert in national security law.
"We don't have all the facts, but under international law, U.S. forces would have substantial discretion to use lethal force given that this was a military operation against an enemy commander likely to pose a very serious threat to U.S. forces," he said.