When, in regard to Robert Mugabe, Gordon Brown says "enough is enough", and George Bush and Nicolas Sarkozy say "he must go", as do the rest of the European Union's leaders, there is a sub-text lurking beneath their words. It is: "Here we have yet another bungling African despot making a grand stuff-up of the nation he is meant to uplift."

The idea of the inept and cruel tyrant has become an archetype in the West's narrative of Africa. As such, it is prejudice; and one of the many things wrong with prejudice, even when it seems to produce an accurate picture of reality, is that it is lazy thinking. It relies on ready-baked concepts than can be slapped onto any more-or-less suitable reality.

And that's just the trouble here. The convenience of seeing Mugabe as a stock-standard incompetent may be blinding the world to something far more sinister. For Mugabe may be, and perhaps should be, held criminally liable for his misdeeds.

The difference between an incompetent whose actions harm others and an outright criminal is a problematic one. This is because an incompetent does not necessarily intend harm to come from his actions. The bungler might even mean well. He might even have been in pursuit of some goal that is, if not actually praiseworthy, understandable.

By contrast, a criminal is thought of as someone who is aware of, or is capable of being aware of, the wrongness of his actions.

The difference matters a lot because society tends to shrug off incompetents in politics as part of the sorry story of human folly, about which little can be done. Criminals, however, awaken very different emotions in us. We want revenge, even if we call it justice.

The question is: which charge fits Mugabe? For, unquestionably, great harm has come to Zimbabwe under his rule. Is he to be held accountable for mere incompetence ... or for criminal liability?

It's important to get it right, because to get it wrong may mean justice denied. That would be justice denied on a grand scale, something for which the world has a rapidly-decreasing tolerance. The answer - a good answer - is not easy to come by. It involves recognition that this is a difficulty that does not begin with Mugabe; it has bedevilled human history. And it involves proof.

The problem was first dealt with by Plato, when he caused Socrates to ask: when a good man kills an evil-doer, of what crime is the good man culpable, and in what measure? Twenty-four centuries later, the problem pulls the historiography of Hitler in different directions: Ron Rosenbaum contrasts, in Explaining Hitler, the differing views of historian Hugh Trevor-Roper, among the first to penetrate Hitler's bunker and the mind of its occupant, and the philosopher and holocaust scholar Berel Lang. Trevor-Roper avers that Hitler was "convinced of his own rectitude". He did evil while believing he was doing good. Lang, on the other hand, insists that the Nazi leader was "deeply aware of his own criminality". Hitler's magisterial biographer, Ian Kershaw, is another who grapples with the issue.

While Mugabe may not be Hitler, and while contributing circumstances and factors may differ in case to case, at the heart lies the question of the awareness of wrong-doing. And it is just there that the difficulty of proof comes in.

In recent days, however, in the case of Mugabe, there has been an interesting development. To my mind, it is of singular help in the bid for an answer.

At a breakfast for journalists in Durban, the secretary general of the ANC, Gwede Mantashe, disclosed that the ANC's National Executive Committee had discussed "Mugabe's fears if he were to relinquish power", according to reports by the journalists present.

Mantashe went on to make two profoundly interesting revelations about that discussion. He said the NEC's view was:

• Mugabe's fears were "real".
• They centred on the example of Charles Taylor, the former leader of Liberia currently being held in The Hague on charges of war crimes and crimes against humanity.
• Mugabe could not be given guarantees he would not suffer a similar fate.

Let us now make some deductions from these disclosures.

The first is that the ANC leadership, more than anyone beyond Mugabe's immediate circle, is in a position to know his thoughts. The contacts between the two have been frequent, and direct. So Mantashe's revelations may be taken as reliable indicators to the dictator's state of mind.

The second is that if Mugabe is likening himself to Charles Taylor ... and is quailing in fear of international justice ... he must be fully aware of the wrong he has been doing. He must know that others know. He must know that his rule has outraged the civilised norms embedded in international institutions of justice.

The prosecution may not be able quite yet to rest its case. But it seems that there are good reasons to conclude that Mugabe is guilty - in the mind of Mugabe himself. In which case, should the world be far behind?

Why, however, would Mantashe have made these startling revelations? Could he be so dull-witted as to not appreciate their import? No, he is not. The answer is right there in what he said - or, rather, in the way he is reported to have said it. The Sapa wire service recorded his words like this: "The Hague has taken a number of African people. Mugabe can't be given any guarantees for his safety in retirement."

These sentences reveal a great gulf of perception between what one might call a Western view and Mantashe's presumably African one. The first of the two sentences reveals Africans' sense of victimhood at the machinations of the West - and, more worryingly, a deep-seated difference in perception of good and evil. After all, the Africans "taken" by The Hague have not been snatched on some whim. (Since its inception in 2002 the International Criminal Court has indicted 12 persons, all of them African. Four are currently in custody. Karadzic is charged before a tribunal specific to Yugoslavia.) In respect of Zimbabwe, too, there is considerable track in a deep difference of perception between the West and Africa.

The second sentence in the statement attributed to Mantashe suggests, especially when read in conjunction with the first, that Mugabe would otherwise deserve guarantees of his "safety" (meaning immunity from prosecution) in retirement.

The overriding implication, then, is that Mugabe is clinging to power not from some lofty, though perverted, sense of mission, nor from a perverse love of power, so much as a means of ducking the law.

In the process of holding on, he has to subvert the political process, persecute and eliminate opponents, and ride roughshod over the needs of his people. The problem is, of course, the longer he hangs on, the more serious his misdeeds become - of necessity.

It must be said that if the prosecution were to rely on only Mantashe's unguarded remarks, a conviction would not be assured. What Mantashe said provides an insight into thinking. It doesn't fully constitute proof.

Once one follows the line offered by Mantashe's revelations, however, the circumstantial evidence starts to accumulate. Some of Mugabe's more outrageous and inane claims take on a perverse kind of logic.

His frequent, and risible, accusations that Britain and other Western states are intent on invading Zimbabwe take a new shape. They become the anxious utterings of the bad guy who fears that the posse is being rounded up to come and get him.

His overt haste to deny the extent of cholera, even to claim it has been quelled, becomes a ploy to keep the West off his patch at all costs.

Something similar may even have informed his moves against Western NGOs up to now. All of these instances and bodies wear the badges of his nemesis - the Western value-set that he fears may call him to book.

Knit these factors together, along with Mugabe's known, overweening desire for acceptance in the West - in Savile Row and in Buckingham Palace - and one has a tapestry of psychological plausibility explaining his actions... even if they don't' make sense, nor are excusable, in the political real world.

There is one, final, strand of inference that might guide thinking in the right direction in apprehending Mugabe's wrongdoing. It may be spurious, but it does tantalise. Of all the world figures who have recently called for Mugabe to go, the two who have expressly said that the Zimbabwean should face international justice, are African themselves: Archbishop Desmond Tutu and the Ugandan-born Archbishop of York, John Sentamu. They appear to be under no illusions about the charge that Mugabe deserves to face. Nor why.