The killing of Osama bin Laden by a team of US Navy Seals has been condemned internationally by lawyers, human rights groups, and European leaders.
United Nations High Commissioner for Human Rights Navi Pillay has also urged the United States to provide full details about what critics have called a summary execution.
"The United Nations has consistently emphasised that all counter-terrorism acts must respect international law," Pillay said.
In London, distinguished human rights lawyer Geoffrey Robertson has described the killing of the al-Qaeda leader as a "perversion of justice" that would rebound on the US.
The Australian-born Queen's Counsel has sat as an appeal judge on a UN war crime court and is one of three jurist members on the international organisation's Internal Justice Council.
He told ABC TV yesterday that the killing of an unarmed bin Laden was not justice.
"It's a perversion of the term.
"Justice means taking someone to court, finding them guilty upon evidence and sentencing them.
"This man has been subject to summary execution, and what is now appearing after a good deal of disinformation from the White House is it may well have been a cold-blooded assassination."
The method of disposing of his body at night without an autopsy was also questionable, he said.
Robertson agreed with other experts such as Ben Wittes, a senior fellow at the Brookings Institution in Washington and Kenneth Anderson, a fellow in national security and law at the conservative Hoover Institution, that the raid itself was legal.
"It's lawful for the United States to be going after bin Laden if for no other reason than he launched an attack against the US," Anderson said.
But Robertson said President Barack Obama had been sloppy with his use of the word "justice" and questions needed to be answered about whether there was an explicit order to kill bin Laden.
He also said the US had given bin Laden what he craved.
"The last thing he wanted was to be put on trial, to be convicted and to end his life in a prison farm in upstate New York," he said. "The way to demystify this man is not to kill him and have the iconic picture of his body. The way to demystify him ... is to put him on trial, to see him as a hateful and hate-filled old man screaming from the dock or lying in the witness box. That way the true inhumanity of the man is exposed."
European Union Home Affairs Commissioner Cecilia Malmstrom said she would have preferred to see bin Laden before a court, and former West German Chancellor Helmut Schmidt said the killing was "quite clearly a violation of international law" that could have incalculable consequences in the Arab world.
Dutch international law specialist Geert-Jan Knoops also said bin Laden should have been arrested and extradited to the US, similar to the arrest of former Yugoslav president Slobodan Milosevic, who was put on trial at the war crimes tribunal in The Hague.
"The Americans say they are at war with terrorism and can take out their opponents on the battlefield," he said. "But in a strictly formal sense, this argument does not stand up."
Reed Brody, counsel at New York-based Human Rights Watch, said it was too early to say whether the US operation was legal because too few details were known.
"Is the world a better place because bin Laden is not here?" he said.
"People can obviously answer that question. But does that mean you have the right to violate protocols of human rights or international law to do that? Then no."
Former Italian Prime Minister Massimo D'Alema, said people should not rejoice at the death of a man, and that the capture and trial of bin Laden might have been a more significant victory than his killing.
But US Attorney-General Eric Holder told the House of Representatives' Judiciary Committee that the acts taken were "lawful, legitimate and appropriate in every way".