The United Nations is supposed to play global policeman, but what happens when its own peacekeepers break the law?

That's a question raised by a string of incidents allegedly involving Pakistani and Bangladeshi peacekeeping troops in war-ravaged Democratic Republic of Congo in 2005.

In a debate this week at the Chatham House foreign policy think tank in London, BBC Africa Editor Martin Plaut presented some of the evidence against the troops, aired in a BBC report in May.

The U.N. mission in Congo, MONUC, which began in 1999, is to date the largest and most expensive peacekeeping operation in the world body's history. Although it has been viewed as a relative success following the end of a conflict described as the World War of Africa, the deployment has also been plagued by allegations of misconduct.

These include sexual abuse of minors, killing of Congolese prisoners and the trading of weapons confiscated from local militias for gold.

The gold-for-weapons scandal came to light following a Human Rights Watch inquiry into the activities of Pakistani peacekeepers in northeastern Ituri province in 2005.

That same year, Bangladeshi forces were accused of beating and killing Congolese prisoners suspected of involvement in a militia ambush near the town of Ndoki in February, which left nine Bangladeshi peacekeepers dead.

In theory, contributing countries should police their own troops, but it remains unclear exactly who should carry out the investigations and which laws should be applied, local or international?

Alex Ramsbothan, a researcher at the Institute for Public Policy Research, said it was difficult to imagine anyone in the U.N. demanding that Pakistani officials bring their personnel to justice as Pakistan is the largest contributor of troops to the U.N.

The country provides 10,000 of the 80,000 troops in U.N. uniform, whereas Britain and the United States only contribute about 300 soldiers each - and not to areas such as Congo. The Bangladeshi contingent numbers about 1,300.

The Chatham House debate offered alarming insights into the United Nations, where internal politics are preventing effective criminal investigations into personnel operating in peacekeeping missions.

The debate heard that senior Human Rights Watch researcher Anneke van Woudenberg first presented the weapons-for-gold allegations to the head of the U.N. in Bunia in December 2005. She pressed the U.N. again on developments in early 2006.

But according to a secret, leaked U.N. document produced by the BBC's Plaut at the debate, an official inquiry was not ordered until August 12, a full eight months after Human Rights Watch presented its findings. To this day, no one has been prosecuted.

The intervention of U.N. troops has doubtless brought more good than bad to Congo. It also needs to be remembered that weapons allegations involve only one Pakistani unit that has since finished its mission.

But in the light of the comprehensive evidence, eyewitness interviews and an inconclusive U.N. investigation, the question of who polices the peacekeepers remains unanswered.

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