Bangladesh’s capital Dhaka is a noisy, exciting city, full of energy and argument. The massive chaos of its constantly stationary traffic is often riven by protests, strikes, marches. These can be on any number of grievances. But this is a country driven by a national agony at its creation which has never been fully addressed. The protest now happening outside the national museum is of an unprecedented nature, and on an unprecedented scale.

Since 5 February, Bangladesh has been transfixed by this ongoing, immense protest. Hundreds of thousands have occupied Shahbagh Square in protest at a verdict passed by the International Crimes Tribunal on war crimes committed during the genocide which preceded the founding of the country in 1971. One of those found guilty, Abdul Kalam Azad, was sentenced to death. Another, however, Abdul Quader Mollah, the assistant secretary general of a Muslim party which collaborated with the genocidaires, the Jamaat–e-Islami, was given life imprisonment. The protests which followed, and are still continuing, are led by intelligent and liberal people; they are, however, calling with great urgency for the death penalty to be passed on Mollah and other convicted war criminals.

The genocide is still too little known about in the West. It is, moreover, the subject of shocking degrees of denial among partisan polemicists and manipulative historians. Before 1971, Bangladesh was East Pakistan, detached from the main body of the country. The founders had believed that the unity of religion would bind it together. Over time, however, the incompatibility of secular cultures had grown overwhelming. Parts of the Pakistani rulers regarded the Bengalis with open racist contempt.

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In his 1967 memoirs, General Ayub Khan wrote that “East Bengalis…have all the inhibitions of downtrodden races … their popular complexes, exclusiveness and … defensive aggressiveness … emerge from this historical background.” This common hostility towards an immensely rich secular culture reached a tipping point when the leader of the nationalist Awami League, Sheikh Mujib, won a national election. He was imprisoned, and the Pakistani forces began a genocide which lasted from March to December 1971.

Pakistan has never accepted responsibility for what happened. Moreover, historians and journalists have come perilously close to genocide denial, or have seemed motivated by a desire to minimise the numbers involved. The official Pakistani estimates were originally only 26,000 dead and 2 million refugees. A recent Oxford historian whose methodology was savagely criticised declared that there were no more than 50,000 to 100,000 dead from all sides in the war.

If this were true, the Pakistani forces would have fallen short of their ambitions. At a meeting on 22 February 1971, the Pakistani President General Yahya Khan is recorded as saying in fury: “Kill three million of them, and the rest will eat out of our hands.” Ten million fled to India; 30 million left the cities and went to the villages.

In the first phase of the war, young men and Hindus, Awami League members, intellectuals, students and academics were targeted for murder. In the second phase of the war, women were singled out. It is thought that at least 200,000 women were raped by the Pakistani forces and their collaborators – 25,000 victims found themselves pregnant, so that is not implausible. There are eyewitness accounts of “rape camps” set up by the Pakistani forces. The numbers, and the names of rape victims, remain disputed. Sheikh Mujib, the first leader of Bangladesh, ordered the destruction of lists so that the shame would not follow the victims all their lives.

In the last week of the war, when Pakistani defeat was inevitable and a new nation was clearly about to be born, a concerted effort was made to kill as many intellectual leaders as possible, many between 12 and 14 December. The names of potential leaders of the future nation to be murdered were found in the diary of at least one Pakistani officer.

Bengali collaborators in the form of armed vigilante groups, Al-Shams and Al Badr, took the lead in these murders, only two days before the war came to an inevitable end.

It is impossible to know the real death toll. The historian R J Rummel, who has looked as deeply into it as anyone, concludes that the “final estimate of Pakistan’s democide to be 300,000 to 3,000,000, or a prudent 1,500,000.” The numbers became politically important in the decades following. As the scholar Bina D’Costa points out, for the Bangladesh government, an upper figure gave the new country greater legitimacy; for the Pakistanis, to scoff and diminish allowed them to demonstrate an ongoing distrust. Whatever the final figure, tens of thousands of those killed died as cruel and appalling deaths as anyone has ever devised. Out of thousands of episodes, one should read the evidence to this trial given by an extraordinarily brave woman, the single survivor of her family. She told how she saw her parents, her two sisters and two-year-old brother killed in front of her before she was raped by 12 soldiers. She was 13 years old.

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That was 40 years ago. The Pakistani perpetrators of the war crimes have never been brought to trial – after independence, Pakistan said that if a single one of its soldiers were tried in the new country, no Bengali then living in the Western half would be given permission to leave. Nor, until very recently, have the Bengalis who collaborated with the genocidaires. The current trials have operated under constant threats of violence from a still active Jamaat-e-Islami. Some war criminals fled abroad. As long ago as 1995, the British authorities had their attention brought to alleged war criminals living in London by a Channel 4 documentary directed by the Dhaka journalist David Bergman. One, Chowdhury Mueen-Uddin, who has been working as an NHS administrator, is only now beginning to be brought to justice.

The shabby series of amnesties and diplomatic effrontery that has left some of the cruellest mass murderers of the century enjoying a peaceful retirement was often challenged by activists, without success. An attempt by the author and national heroine Jahanara Imam to promote war crimes trials in 1992 did not succeed. The International Crimes Tribunal was finally established only in 2008. Its work is slow, and everyone feels that it is achieving what it can before the government changes at the next election. There is no faith at all that Khaleda Zia, the leader of the opposition and, it is often asserted, an ally of the Jamaat-e-Islami, would allow the Tribunal’s work to continue for a day, or let its sentences stand.

The rage of the crowds at the life sentence given Mollah is that they know, as so often before, that Sheikh Hasina’s government has not achieved what it could, and a change of government will almost certainly lead to a pardon of imprisoned war criminals. It has done so often in the past. Hence the call for the death penalty, as the one punishment that no politician can reverse.

The calls for the death penalty are the counsel of despair. These are people who believe passionately in the rule of law, and justice. They have seen too many times that justice is only done at the bidding of politicians, and may be undone. But the chaos of the Mollah trial has stirred great concern from observers, and from thoughtful Bengalis. The pressure of the Shahbagh protests has encouraged Sheikh Hasina’s government to intervene, proposing the possibility of prosecution appeals, in the interests of securing the death penalty. More intervention in justice by politicians; more judicial murder; more martyrs. It is important, above all, that democratic states reveal themselves to be better than the brutes who murdered and raped, and did their utmost to extinguish a people. And yet the probability that some of the worst war criminals in history will never face justice, and the worst of their collaborators will only have to face a year or two in prison, drives the protesters to despair.

What is the solution? Serious doubts have been raised about aspects of the trials, and the death penalty cannot be the right solution. But life imprisonment in Bangladesh for the mass murderers commands no respect.

There is one further possibility: the Liberian war criminal Charles Taylor was not imprisoned in Liberia, but under the provisions of the ICC in The Hague. The intervention of international law-makers ought to be desirable, and to take murderers out of the control of national politicians. That might permit, too, the trial of the main war criminals, and not just their Bangladeshi collaborators.

The Bangladesh atrocities are too important to go on being manipulated when a government changes. It seems as if this convulsive national exorcism, if it is to achieve justice, must take place in the eyes of the world, and with the world’s input. For the rest of us, we have averted our eyes for too long. We have a duty to learn about this forgotten genocide, and face our own responsibilities squarely – not to shelter murderers, not to ignore, not to forget.

'Butcher of Mirpur'

Abdul Quader Mollah, the assistant secretary-general of Bangladesh’s Jamaat-e-Islami party, sparked protests when he emerged from Bangladesh’s Supreme Court on 4 February having been handed a life sentence for his role in the atrocities committed during the 1971 war for independence. He was clearly happy with the ruling - giving a victory sign to supporters outside the court. But critics of the so-called “Butcher of Mirpur” - who was convicted of of beheading a poet, raping an 11-year-old girl and shooting 344 people – have been left fuming over the sentence, and are calling for him to face the death sentence, like fellow accused Abul Kalam Azad.