"Making the rounds in Khartoum," HRW Executive Director Kenneth Roth recounts in an article for The Financial Times, "I sensed that serious threat of prosecution at the ICC could help Darfur."

To this day, government-sponsored militias in Darfur, known as the Janjaweed, have been on a rampage of rape, arson and murder. The perpetrators are largely landless Arab nomads, the victims mainly non-Arabs. Already some 70,000 have died and some 1.5m have been displaced. What will it take to end this assault, let alone create conditions for peace and security?

Part of the solution lies in the 3,500 troops the African Union has offered to provide protection. But their deployment has been painfully slow and in Darfur's vast, harsh terrain, they at best will be able to guard camps for the displaced and respond belatedly to attacks elsewhere. Sudan's government has refused to carry out the essential task of disarming and disbanding the Janjaweed militia, its first line of defence against rebel forces in Darfur. With AU-sponsored peace talks stalled and ceasefire violations rife, the stalemate is unlikely to end soon.

In the meantime, international prosecution could help. In September, the Security Council established an international commission of inquiry for Darfur, which reports in January. Given the magnitude of the crimes perpetrated, the commission is likely to recommend that the Security Council refer Sudan to the International Criminal Court—the new forum for prosecution of genocide, war crimes and crimes against humanity.

The ICC's potential to change the political dynamic in Sudan became apparent when I met senior Sudanese officials in Khartoum last month. They first claimed that as victims in Darfur do not know the names of their attackers, the government cannot possibly know whom to prosecute. Why not begin with Musal Hilal, widely acknowledged as the Janjaweed's leader, I suggested. "No one has filed a complaint against him," was the reply. It was an excuse I heard repeatedly.

When my offer to file a complaint myself was rejected, I mentioned the ICC — and the smiles vanished. The court, I explained, is concerned less with low-level attackers than with those who direct atrocities. The government, I noted, knows their names. Groups such as Human Rights Watch could provide a catalogue of the crimes that establish a pattern of atrocities to which commanders could not have been oblivious. Under principles of command responsibility, that is sufficient for prosecution.

Making the rounds in Khartoum, I sensed that serious threat of prosecution at the ICC could help Darfur. Sudanese officials know the court defers to efforts at national prosecutions only if they are made in good faith. Khartoum's passive approach to prosecution does not begin to meet that test. If the ICC takes up Darfur, the government would have to begin high-level prosecutions or, as in Bosnia when an international tribunal launched its own prosecutions, abusive leaders would be marginalised as they tried to evade arrest. Either result would help curb the violence.

The Security Council has yet to refer any case to the ICC—largely because the US objects to the court's theoretical power to prosecute Americans. Darfur, however, could be the first such referral. The US has taken a strong stand and described the Darfur killings as genocide. It might pay a high political price for vetoing a Security Council referral. The US is not the only obstacle. China's oil interests in Sudan make Beijing reluctant to endanger the Sudanese officials behind the Janjaweed. Yet, ending the killing would help prevent the conflict from disrupting oil supplies. And China should be reluctant to be the sole obstacle to helping Darfur.

European governments also worry that ICC prosecutions of senior officials might disrupt efforts to end the separate 21-year war in southern Sudan. But experience shows that peace built on impunity for ongoing atrocities is often short-lived. Indeed, the failure to prosecute those behind atrocities in southern Sudan arguably laid the groundwork for today's atrocities in western Sudan.

By signalling that ethnic cleansing is not tolerated, prosecution would be a big step towards creating conditions in Darfur for the displaced to return home. Prosecution alone will not solve the problem, but it is vital to a durable solution. If the Security Council wants lasting peace in Darfur, it should affirm its determination to see those responsible for crimes against humanity there brought to justice.