It's good to see bad guys behind bars.

Especially if they're convicted. Justice is better than revenge. And justice must be done for the relatives of the victims as well as for the dead. Part two of the Mubarak trial this month was a case in point. Egyptians want to know exactly who ordered the killing of innocent demonstrators. Who was to blame? And since the buck stops – or is meant to stop – at the president's desk, how can Mubarak ultimately escape his just deserts? The same will apply to Gaddafi when – if? – we get him.

Ben Ali? Well, he'll stay, presumably, in his Saudi exile – which is anyway as near as you can get to a death sentence – since his in absentia trials in Tunis were travesties of justice. Bashar al-Assad? We shall see if we need him or not. Gaddafi? Probably better dead than sent to trial, because he would probably do a Milosevic, mock the court and die in custody. Please note that no tribunals have called for the princes and emirs of the Gulf, or the Plucky Little King of Jordan, or the weird President Bouteflika of Algeria and his henchmen, or the much creepier President of Iran, to be put on trial.

When we decided to keep Hirohito on his Japanese throne, we winnowed down the number of Japanese war criminals to be hanged. Oddly, it was Churchill who wanted the worst of the Nazis to be executed on the spot; it was Stalin who wanted a trial. But then again, Stalin wasn't going to be accused of the mass murder of millions of Soviet citizens, was he?

It all depends, I think, on whether criminals are our friends (Stalin at the time) or our enemies (Hitler and his fellow Nazis), whether they have their future uses (the Japanese emperor) or whether we'll get their wealth more easily if they are out of the way (Saddam and Gaddafi). The last two were or are wanted for killing "their own people" – in itself a strange expression since it suggests that killing people other than Iraqis or Libyans might not be so bad. In other words, civil war killers are just as likely to end up on the hangman's noose.

Or are they? In Lebanon, for example, things aren't that simple. While America would like to know who planned the bombing of its Beirut marine base in 1983, killing 241 US servicemen, it has no war crime trials planned. Nor do the Lebanese. In fact, two amnesties for killers of the 1975-90 civil war specifically exempt all murderers from trial except those who killed religious or political leaders. An interesting distinction.

If your mum and dad were butchered by a crazed neighbour who happened to be of a different religion, the murderer will not go to court. If, however, he knocked off the local priest or imam, he has no immunity. Lebanon's 1991 amnesty, for example – Article 3 for those who like to peek into legal inanities – stipulates that amnesties do not apply to those who commit "the assassination or attempted murder of religious dignitaries, political leaders, Arab and foreign diplomats". Lebanese law, in other words, bestows more value on the life of a bigwig than a prole.

As the Lebanese jurist Nizar Saghiyé puts it: "We have to forget collective massacres, crimes against humanity, ordinary victims – only the murder of a leader is supposed to be punished." When a Lebanese parliamentarian pointed out that this denied the constitution's insistence on equality before the law, the Lebanese president declared that a politician was a "national symbol". This also means that political leaders who have ordered torture and mass murder – of course, I meet them socially in Beirut today – are safe from prosecution. The killers of up to 150,000 Lebanese are also safe, unless they tried to knock off a bishop or a sayed or a warlord.

Just why civil wars are so cruel – and thus, surely, deserving of even more condign punishment – remains a legal mystery. In his preface to Aïda Kanafani-Zahar's splendid analysis, Liban: La guerre et la mémoire (Lebanon: War and Remembrance), Antoine Garapon suggests that because love is the opposite of hate, the most fraternal of communities can become the most murderous: "The cheerful neighbourliness between the (religious) communities – which is the glory of Lebanon – becomes its hell." Thus the Lebanese civil war was "a crime of passion", he says. Kanafani-Zahar draws attention to the fact that the murder of Christian Maronite president-elect Bashir Gemayel in 1982 was followed only a few hours later by the massacre of up to 1,700 Sabra and Chatila camp Palestinians by Israel's Phalangist allies (Gemayel being their now dead leader); yet only Gemayel's assassination was referred to the Lebanese "Council of Justice".

In Bosnia, criminals continue to be sought, although the war had much in common with the Lebanese conflict. Lebanese Christians usually supported the Croats (the Phalangists sent them weapons) while Arab Muslims naturally sympathised with the Bosnian Muslims. In Lebanon, however, there were official village "reconciliations", attended by Muslim and Christian prelates and political leaders. Not so in Bosnia.