What are the chances that Hosni Mubarak will stand trial for crimes committed as president of Egypt?
We do not need to look very far — at least in geographical terms — for a precedent: at the end of last year, a court in Tel Aviv found Moshe Katsav guilty of rape when he was a minister in the Israeli government and further sexual offences while he was president.
But just as Katsav was not much of a president, that is not much of a precedent: Egypt is unlikely to become a pluralist democracy like Israel, where two judges on the court that convicted Katsav were women and the third, who presided, was a Christian Arab. And if Mubarak is to face trial, it would presumably be for using state power to crush his enemies.
While in office, heads of state normally have immunity from prosecution for acts done as part of their official duties. Under international law, this immunity extends to serving diplomats, foreign ministers and perhaps defence ministers. Without it, the conduct of international relations would be impossible. But individuals lose these "personal" immunities when they leave office.
International law also recognises so-called "functional" immunities for various state officials acting in the exercise of their functions. Since their actions are attributed to the state itself, the immunities continue after the individual retires.
But Micaela Frulli, writing in the Oxford Companion to International Criminal Justice, says: "It is almost universally shared that functional immunity from foreign jurisdiction cannot be invoked by those who allegedly committed one of the so-called core crimes: war crimes, crimes against humanity, acts of torture and genocide."
This principle was recognised by a majority of the law lords who dealt in 1998 and 1999 with the case of Augusto Pinochet. The former Chilean dictator failed to persuade the UK's highest court that he had immunity from extradition to Spain to face charges of torture and hostage-taking.
And the same principle is to be found in the treaties governing international criminal tribunals. Take, for example, the Special Court for Sierra Leone, a hybrid court set up by agreement between Sierra Leone and the United Nations and currently sitting at a borrowed courtroom in The Hague.
The court's statute says that "the official position of any accused persons, whether as head of state or government or as a responsible government official, shall not relieve such person of criminal responsibility nor mitigate punishment".
As a result, Charles Taylor, the former president of Liberia, is on trial before the court for crimes against humanity.
Similarly, the International Criminal Court operates under a statute that "applies equally to all persons". In particular, "official capacity as a head of state or government ...shall in no case exempt a person from criminal responsibility under this statute". It is on this basis that the court's hapless prosecutor has sought, so far without success, to have President Omar al-Bashir of Sudan arrested for genocide, crimes against humanity and war crimes.
Perhaps not surprisingly, Egypt is not among the 104 countries that have accepted the court's jurisdiction. Neither is Israel or the United States. But that does not mean that their former leaders are safe.
Many countries claim jurisdiction to put defendants on trial for very serious crimes, even if they were committed abroad and even if the defendant is a foreigner. Defendants can be prosecuted for these "offences of universal jurisdiction" even if they have no links to the prosecuting state.
Under legislation passed in 1957, it is an offence under English law to commit a "grave breach" of the 1949 Geneva Conventions anywhere in the world. It was on this basis that various Israelis have recently avoided visiting London, concerned that they might be arrested for war crimes.
No prosecution can be brought without the consent of the Attorney General but his consent is not required for an arrest warrant. Under legislation currently before parliament, the Director of Public Prosecutions would have to give his consent before a warrant could be issued.
At the beginning of February, it emerged that George W. Bush had called off a trip to Switzerland, where he was to have promoted his autobiography and addressed a fund-raising dinner for Israel. The campaign group Amnesty International said it had sent Swiss prosecutors a detailed analysis of allegations that the former US president had been responsible for authorising torture of detainees held at Guantanamo Bay. Bush has denied that waterboarding — simulated drowning — amounts to torture.
It is far too early to say whether Mubarak will face the courts. But, as Pinochet, Bashir and now Bush seem to have found, in a legally dangerous world it's sometimes best to stay quietly at home.