KILLING quickly in combat, when large numbers of soldiers are fighting according to the laws of war, is sad but legal. Change any of those parameters, and things get tricky. Some lawyers have denounced the killing of Mr bin Laden, unarmed and in his home, as an extra-judicial murder. Others see it as a wholly legitimate military operation.

Every country allows soldiers to use lethal force against a declared enemy in wartime, just as police may, in some circumstances, kill criminals. But America is at war with an organisation, not a country, and though al-Qaeda is not a state it is (by its own account) at war with the United States. Purists argue that the criminal law is the right weapon for defence against terrorists; pragmatists would differ.

In any case, America's armed forces have legal backing for their actions against al-Qaeda. Though a presidential order of 1976 bars assassinations by America's spooks, an act of Congress in 2001 authorised the president to use “all necessary and appropriate force” against the perpetrators of the terrorist attack in September of that year.

Next comes the category of person killed. Deliberately targeting civilians in any conflict is illegal. But al-Qaeda has a quasi-military structure, and plenty of precedents exist for killing enemy commanders in wartime: in April 1943 America ambushed Admiral Isoroku Yamamoto, the Japanese naval commander, on the express orders of President Franklin Roosevelt. Critics of America's actions are arguing that Mr bin Laden was no longer the effective commander of al-Qaeda. But that would be hard to prove.

Location can be controversial too. Russia sees the émigré Chechen leadership, for example, as legitimate targets and has killed them in places such as Qatar, to the fury of the local authorities. The assassination of Mahmoud al-Mabhouh, a Hamas commander, in Dubai in January 2010, presumably by Israel, aroused similar ire. But Pakistan has itself used lethal force against al-Qaeda and allowed American drone attacks, for all its loud complaining now.

Timing complicates the question further. Bombing soldiers in a hospital, or shooting them after they have surrendered, is a war crime. Soldiers are under no legal duty to give their opponents a chance to surrender, though if the white flag is shown it must usually be honoured. Nobody has suggested that Mr bin Laden tried to surrender. But his shooting while unarmed raises questions about the nature of his resistance. Any video footage of the attack will be closely scrutinised to see whether he was a combatant, rather than a prisoner.

Behind the controversy is a change not in the laws of war but in the means of waging it. Drone strikes were measured in dozens under George Bush. They number many hundreds under Barack Obama. They allow an official sitting in America to kill someone thousands of miles away. Such killings usually escape scrutiny—and controversy—because they preclude any chance of surrender. Killing someone in the same room is always going to be more complicated.