A lawyer who served as a prosecutor at the Nuremberg trials after World War II says Osama bin Laden should have been put on trial.

American lawyer Benjamin Ferencz, now 91, has written a letter to the New York Times, questioning whether the death of the terrorist leader was justifiable self-defence or premeditated illegal assassination.

He says the Nuremberg trials earned worldwide respect by giving Hitler's worst henchmen a fair trial so that truth would be revealed and justice under law would prevail.

And 65 years later he says the US should again have supported a trial of the world's most wanted international criminal bin Laden.

"It's a right that we give to every mass murderer and always have," he told the BBC.

"This is what distinguishes us from the tyrants."

There have been several revisions to the official account of what actually happened at the compound in Abbottabad in Pakistan this week.

Earlier official reports of the death of bin Laden said he was killed after resisting and using his wife as a human shield.

But the White House now says those details are not correct.

Officials say after US Navy Seals found bin Laden in a bedroom with his wife, he gave no signal of surrender and was shot in the head and, some outlets also report, in the chest.

His wife reportedly tried to come in between him and the commandos and was shot in the leg.

Law of armed conflict

Mr Ferencz says if the shooting of bin Laden was not a result of self-defence then it was illegal.

"Here the difficulty is that we have releases from the government which are changed daily," he said.

"I can understand the need for secrecy but the issue here is whether what was done was an act of legitimate self-defence or whether it was not.

"And killing a captive who poses no immediate threat is a crime under military law as well as all other laws."

But associate professor of international law at the Sydney Law School, Dr Ben Saul, disagrees.

He says it would have been illegal had bin Laden been trying to surrender.

But Dr Saul says if not, under international law the US had the right to kill bin Laden, because he was effectively the military commander of an organisation waging war on the US.

"In armed conflict members of national armed forces like Australian soldiers and soldiers of other governments can be killed because they're soldiers," he said.

"They don't have to have weapons in their hand at the time that they can be lawfully killed.

"They can be killed whilst sleeping in a military barrack, whilst eating in the mess kitchen or even whilst in the shower or on the toilet.

"The fact is under the law of armed conflict if you're a member of an armed fighting force you can be killed, that's the price you pay for participating in armed conflict."

Announcing the death of bin Laden, US president Barack Obama said when he first came to office he ordered the CIA to make the killing or capture of bin Laden the top priority in its war against Al Qaeda.

Reuters has reported that the commandos were under orders to kill Osama bin Laden, not capture him.

Mr Ferencz says he should have been captured.

"If you have a belief in the rule of law, as I do, and I believe that it's a sole way of creating a more humane and peaceful world, then you must give every defendant the right to be heard," he told the BBC.

Dr Saul says the US was not legally obliged to capture bin Laden.

"If under the law of war there's a right to kill somebody because they're involved in hostilities as a military commander then there's no obligation, as there is in peacetime, to try to affect a kind of law enforcement arrest in the first place," he said.

"I think there may well be good policy reasons why it would have made good sense for the US to try to arrest bin Laden and put him on trial.

"That kind of policy choice is quite different from the legal question."