After receiving news that a team of US Navy Seals had shot dead Osama Bin Laden at a compound in northern Pakistan, President Barack Obama announced that justice had been done.
The demise of the man held responsible for mass atrocities, including the 11 September 2001 attacks, was welcomed around the world.
But as the US narrative developed - and changed - after the raid, there were growing questions about whether it was legal to kill the al-Qaeda leader.
At one level, these have focused on what happened during the operation at the building in Abbottabad in which Bin Laden was found.
"The issue here is whether what was done was an act of legitimate self-defence," said Benjamin Ferencz, an international law specialist who served as a prosecutor during the Nuremburg trials and argued that it would have been better to capture Bin Laden and send him to court.
"Killing a captive who poses no immediate threat is a crime under military law as well as all other law," he told the BBC World Service.
US Attorney General Eric Holder has led the case for the defence of the operation, which he said was a "kill or capture mission" and "obviously lawful".
"If there was the possibility of a feasible surrender, that would have occurred," he told the BBC, adding that the protection of the Navy Seals was a priority.
"One does not know what Bin Laden had there," he said.
"It's one o'clock, two o'clock in the morning or so, it's dark. This is a mass murderer who's sworn to continue his attacks against the United States and its allies.
"When confronted with that person, in the absence of some clear indication that he was going to surrender, I think that they acted in an appropriate way."
A clear picture of the exact circumstances in which Bin Laden was shot has not emerged, and may never do so.
US officials have suggested that the al-Qaeda leader may have been reaching for a weapon, and that the Navy Seals were wary that people in the compound might have been wearing suicide belts.
But they have also said Bin Laden was not carrying a weapon - after initially saying he was.
And they have told US media that just one person in the compound shot at the special forces team, in what appears to have been a one-sided confrontation.
Legal experts have therefore asked whether the US forces were instructed to kill, and whether Bin Laden was offered a chance to give himself in.
Like Mr Ferencz, British law professor Philippe Sands QC says it is impossible to make a definitive legal judgement without knowing precisely what happened. But he says the case for the raid's legality has been weakened.
"The question to ask is: were the measures taken in the actual situation that pertained reasonable and proportionate, given the circumstances in which the [Navy Seals] found themselves?" he told the BBC.
"The facts for Bin Laden don't appear to easily meet that standard."
On a broader level, US officials have justified Bin Laden's killing as an act committed as part of an armed conflict with al-Qaeda.
Mr Holder said Bin Laden's killing was "not an assassination" but rather "an act of national self-defence" against an al-Qaeda leader who had acknowledged his role in the 9/11 attacks.
"You have to remember, it is lawful to target an enemy commander," he said.
Some legal experts have backed up that position.
"I don't think that this is an extrajudicial killing," Philip Bobbitt, a US specialist on constitutional law and international security, told the BBC's World Tonight programme. "I think this is part of an armed conflict authorised by the United Nations, authorised by both houses of Congress."
The extent to which Bin Laden could have still been a key commander, given the restrictions on his movements and communications, has been queried, though the US has said he was "active in operational planning" from Abbottabad.
But the location of the raid has also raised questions. Bin Laden was killed in a normally quiet town, in a country with which - despite ongoing military operations including drone strikes near the border with Afghanistan - the US is not officially at war. And Pakistan was not given prior warning of the raid.
"As a matter of international law, one country is not free to enter another country apparently without the authorisation of that country, and intervene, whether to kidnap or kill a national of a third state," Mr Sands said.
He acknowledged that under what is known as the doctrine of necessity, where there is an "overriding threat to national security", such an act might not give rise to responsibility or liability.
But he said the difficulty with that argument was that it comes against a background of a rise in extrajudicial killings, including through the use of drones, and that this was not a "lawful direction to be taking".
The logical conclusion of any idea that Bin Laden could be killed as an enemy combatant was "that anyone associated with al-Qaeda in any country in the world can be taken out, can be executed," Mr Sands said.
"I think it's deeply troubling if we are indeed moving to a place where you can have a global assassination policy for those who are perceived to cause trouble," he added.
The UN special rapporteur on extrajudicial, summary or arbitrary executions, Christof Heyns, and the special rapporteur on the promotion and protection of human rights and fundamental freedoms while countering terrorism, Martin Scheinin, have raised a similar concern.
"In certain exceptional cases, use of deadly force may be permissible as a measure of last resort... including in operations against terrorists," they said in statement.
"However, the norm should be that terrorists be dealt with as criminals, through legal processes of arrest, trial and judicially decided punishment," they added.
"Actions taken by states in combating terrorism, especially in high profile cases, set precedents for the way in which the right to life will be treated in future instances."
Potentially, Bin Laden's killing could be challenged under international, Pakistani or US law, though for now there seems little prospect of any serious legal case being brought.