Hundreds of thousands of people were massacred during the genocide of 1994 in Rwanda. Now, in the crucible of the ensuing war in neighbouring Congo, the fugitive killers are training their children to carry on the Hutu mission of extermination, and awaiting their opportunity to return to the mother country.

The boy with the shaved head and Kalashnikov slung across his legs is uncertain about a lot of things, even his age. He pulls at the long, dry grass around him and in a quiet voice says he thinks that he might be 13 years old because he was a baby when his mother wrapped him with the last of her possessions and made her escape across the border. Asked where he is from, he gestures toward the lush hills rippling to the east. Somewhere among them is an unmarked frontier with a country the boy calls home, although he has no memory of the last time he was there.

What’s over the hills? Rwanda, he says. Where are his parents? He doesn’t know. Dead, he thinks. He doesn’t remember them, only what some people told him.

And what was he told? He was very small when everyone ran away from those they called the inyenzi - the cockroaches. His mother carried him across the border, out of Rwanda. But then something happened to her. Perhaps she was among the multitudes who died then or in the ensuing years; he was left alone and the other people in the refugee camp looked after him. His father was a soldier. He just disappeared. No one said anything about him.

That was in 1994 and the boy has been on the move ever since, tramping from one part of the Democratic Republic of Congo to another, growing up as part of a caravan of killers and their families who, for a long time, dared not stay still if they wanted to survive, until he came full circle to the place where he was separated from his mother.

He falls silent again for a while, watching Congolese villagers who live in fear of children such as him. Then he begins to speak about what he does know. It is the Tutsis, those inyenzi, who are to blame for his predicament, he says, and he must kill them. He hates them all. They stole his country, Rwanda - a Hutu country, he calls it - and he wants them dead.

There is an innocence to the boy’s face for all the hardships he has endured, but there is something in his voice with that word, inyenzi. A sharpness, perhaps out of contempt or perhaps knowing its power to conjure up the horror of the murder of hundreds of thousands of Tutsis in the Rwandan genocide of 1994 by men who branded them "cockroaches". Soon afterwards, when Tutsi rebels defeated the killers and took over Rwanda’s government, the Hutu exodus began and the boy’s life changed irrevocably.

Child soldiers can be found across Africa. Sometimes they are responsible for appalling atrocities; sometimes it is because their minds have been twisted by powerful drugs. But nowhere on the continent are they as driven by hate and ideology as among the Rwandan Hutu refugees in eastern Congo. Here, after more than a decade of invasion, civil war and slaughter - rooted in the genocide - a second generation of killers is being imbued with the mind-altering ideology of extermination and reared to hate and murder Tutsis.

Some of the children learn it from fathers who were responsible for the mass killings the first time around, back in Rwanda. Others, like the boy, are raised by the extremist Hutu rebels who control large areas of eastern Congo and are among the most important causes of the conflict there that has claimed an estimated five million lives or more over the past decade and continues to kill about 45,000 people each month in Congo through the effects of war - principally starvation and disease.

These children are led by men with multimillion-dollar rewards on their heads offered by the United States for their capture to stand trial accused of the murder of thousands in the 1994 Rwandan genocide. America has listed their armed group, the Democratic Forces for the Liberation of Rwanda (FDLR), as a terrorist organisation, but some of its political leaders have found safe haven in Europe. And while their army is fighting, the leadership is raking in millions through the smuggling of gold and diamonds, and extortion.

The boy is sitting alone, guarding the perimeter of an FDLR camp that is a bone-shaking six-hour drive into the mountains south of the Congolese city of Bukavu on unmade roads that wind along the border with Rwanda and then veer in country. The Congolese government has almost no influence in these parts. Its forces rarely venture into the surrounding hills and the FDLR lives off the local people - plundering and sometimes raping and killing.

The camp is little more than a dozen or so mud brick and wood huts with grass roofs.

A handful of soldiers sit around. Some wear the same uniforms as government troops - plain olive green, with black boots or wellingtons. Others sport brightly coloured T-shirts with slogans promoting various beers. They carry Kalashnikovs and a couple of larger-calibre weapons with belts of bullets slung across shoulders. There is a weak attempt at camouflage with grass stuck into baseball caps, but the camp is isolated on the side of a hill, not visible from the approach road and easy to protect. No one comes after the FDLR here, but there is a rusting rim of an old car wheel dangling from a nearby tree as an alarm. The boy is supposed to beat it as hard as he can if the enemy approaches.

He looks to be the youngest fighter here - most of the others are in their late teens or 20s although one man with a large paunch seems out of place. A couple have weak moustaches, others shaved heads.

They are all members of the FDLR’s armed wing, known within the organisation as the "Army of Jesus". The religious undertones run deep. One of the group’s operations against Rwanda was codenamed "Oracle of the Lord".

The FDLR boasts about 7,000 fighters, hundreds of them children or youths, and is the largest of the militias in eastern Congo.

It controls about one-fifth of the two vast provinces that border Rwanda - North and South Kivu - but its influence ranges considerably further as it hunts down Tutsis who live in Congo, and continues to threaten nearby Rwanda.

The boy, with his straightforward beliefs, sees no reason not to say aloud that the path to a better life lies over the graves of Tutsis. It is a philosophy based on the "Hutu 10 Commandments" that underpinned the genocide. The commandments call any Hutu who marries a Tutsi a traitor, and say that the Tutsis’ "only goal is ethnic superiority".

"Hutu must stop taking pity on the Tutsi," says the eighth commandment.

"Hutu must stand firm and vigilant against their common enemy: the Tutsi," says the ninth.