Killing people may lawfully occur in self-defence (by people or states), in lawful combat in the context of an armed conflict, or by a morally questionable but lawfully applied death penalty. That is not to say that assassinating state enemies does not take place. It is practised, most notably and openly by Israel but also by the United States and others, and has been for many years. But that does not make it legal. Bin Laden's killing, as immediately satisfying as it may seem, has started to raise some perplexing issues. The facts now point towards a planned execution and do not reflect initial statements by the US that the operation left open the possibility of capture. Leaders, including our own, are calling this ''justice''. But is this what justice means? To be sure, justice is not just a legal concept, it is also a moral one. If bin Laden could have been captured, should he not have been tried in a properly constituted court of law? In this way, he could have been forced to suffer the same ignominy as other tyrannous leaders in recent years - Slobodan Milosevic and Saddam Hussein in particular. Not only would this comport with common conceptions of justice, but it would allow the world to watch the terrorist mastermind rant, rave and ultimately wilt before live court cameras. Of course, this is not everybody's idea of justice. Why should bin Laden be given any more compassionate treatment than his thousands of victims, who were truly innocent? Does not one view of justice accord with the killing of such a man, untested in a court of law. After all, we all know what he did. Leaving bin Laden for a moment and turning to the suddenly forgotten war in Libya, this too raises similar questions about how we conceptualise and apply ideas of justice and morality.

NATO is in Libya on a UN Security Council mandate, strictly limited to the creation through air power of a no-fly zone and to protect civilians and the civilian population of Libya from Gaddafi's military and security forces. While there is much debate about the extent of the UN mandate, it seems certain that the targeted killing of Gaddafi is not envisaged or encapsulated in resolution 1973. But that is precisely what NATO's strike on a house in Tripoli on Saturday appeared to be aimed at. This seems all the more credible following clear statements by US and British leaders that, however the military action in Libya unfolds, Gaddafi must go. That sentiment is likely to be shared by many, but the murder of the country's leader is a different matter altogether. Targeting Gaddafi might be said to be militarily legitimate where a state of all-out war against a country is in train - he is, after all, the commander-in-chief of Libya's armed forces. But that is not NATO's legal mandate and had this been an element of the Security Council's plan, the resolution to use force against Libya would most certainly have been vetoed by Russia and/or China. If bin Laden could have been captured, should he not have been tried in a properly constituted court of law? That means intentionally targeting Gaddafi may be no more legal than the targeting for assassination of Osama bin Laden.

It is tempting to respond to such legal perambulations by saying: so what? Killing bin Laden or Gaddafi is a good thing - they are evil men with untold blood and misery on their hands. But is that not precisely what separates ''us'' (those who believe in the value of life, the rule of law and fundamental human rights) from ''them'' (murderous hateful souls such as bin Laden and Gaddafi)? As the International Criminal Court prepares to issue arrest warrants against Gaddafi (acting in line with the now almost forgotten Security Council resolution asking the court to investigate and prosecute crimes in Libya), we could be talking about arresting and transferring Gaddafi, and charging and trying bin Laden in a court of law. This would be a true symbol of the power of democracy and the rule of law. Instead, we are talking about the assassination of leaders and terrorists we revile. Let us be clear - the targeted killing of bin Laden and Gaddafi is unlawful. Whether it is moral depends, I suppose, on your point of view. But as we celebrate bin Laden's demise, we should also reflect on who might be the target of such extrajudicial killings if the balance of the world's power lay not with the US and the West, but with other emerging and powerful nations. The rule of law is there for a reason - to protect everybody from the excesses of unchecked power. Gideon Boas is associate professor and Pascale Chifflet is a sessional lecturer at Monash University law school.