The investigation stretched across three continents: Europe, America and one of the most dangerous places in the world, the Democratic Republic of Congo, in Africa.
By Raphael Rowe
Watch Raphael Rowe's report on Panorama: Mission Impossible at 8.30pm on BBC One Monday 28 April 2008
It was in DR Congo that I visited two of the most dangerous rebels in prison awaiting trial for war crimes.
Gen Mateso Nyinga, known as Kung Fu and Col Drati Massasi, known as Dragon.
These men stand accused of killing men, women and children.
It just so happened that the day of my visit fell on my birthday.
Ironically having spent 12 birthdays in prison, up to the age 32, as a miscarriage of justice, I never in my wildest dream thought I'd be inside on my 40th.
The prison guards wore uniforms and clutched weapons but showed no interest in security.
They didn't even rise from their white plastic chairs to pat me down.
Floribert Njabu is president of the militia group FNI
If they had, they may have found the small digital camera in my pocket.
Investigators for the United Nations had been to see these men before me.
They were following information they'd been given from witnesses that Pakistani peacekeepers had returned decommissioned weapons to these rebels.
In a report, the UN concluded they had conducted inquiries to identify credible evidence, but were unable to locate any witnesses who had seen the peacekeepers providing weapons to the militia.
The report went on to say that during interviews with the UN investigators, Kung Fu and Dragon denied receiving weapons or ammunition from Pakistani peacekeepers.
Two months before this report was made public the rebels had issued a statement admitting they had been given weapons from the peacekeepers.
The UN investigators did not go back to question the rebels to establish why they had changed their evidence. So I did.
Inside the prison compound, it was hard to tell the difference between prisoner and visitor.
Gen Mateso Nyinga, known as Kung Fu awaits trial for war crimes
Chickens and goats wandered aimlessly in the dust as men, women and children attended to small plots of grass from which they grew what they could.
I was led unprotected, to the higher security complex where I was introduced to Floribert Njabu, president of the FNI militia group.
The ethnic Lendu militia was involved in the bitter clashes with their Hema rivals in the Ituri district in the eastern DR Congo during the long war there.
Njabu led me through a corridor of men into the cell complex guarded by high concreted walls.
The smell of sewage mixed with the sweat from the prisoners and scent of alcohol was powerful.
The walk to meet Kung Fu and Dragon was not easy.
We were aware that these men were killers and most of those we passed were former rebels capable of barbaric crimes.
At the end of a narrow concreted corridor with little light coming in through barred windows I was introduced to commander Kung Fu and then Dragon.
Their eyes were deep red, burnt by the coal they burn to cook food.
'Dragon' is accused of killing men, women and children
Thousands of civilians lost their lives when these rebel leaders were in command.
If what they confessed to me for the first time in a recorded interview from the confines of a prison cell is true, the reputation of Pakistani peacekeepers and the UN will be damaged beyond repair.
When I finished the interview and was leaving, a small entourage of FNI rebel commanders and ex-combatants slowly walked behind the footsteps of Njabu their president as he escorted us to an invisible point at which he told us he could not go beyond.
The three hours I was with these men was a strange experience. They were clearly in control, and I felt they could overpower the guards if they wanted to.
Panorama: Mission Impossible, BBC One 8.30pm Monday 28 April 2008.