Image caption US agents rely on locals to provide information about suspect Americans

As part of an initiative to protect children from sexual predators, including those who travel overseas, special US agents operating in South East Asia have brought more than 80 alleged child sex tourists back to America to face justice.

Sihanoukville looks like paradise, or at least a decent, low-rent version. Golden beaches, swaying palm trees, cheap alcohol and shimmering sea.

Retired American pharmacist Ronald Adams had come here for the good life - setting up a beachside cafe. But one morning last February Adams' personal vision of paradise was shattered, when officers from the Cambodian National Police raided his apartment.

They found a collection of sex aids, child pornography on DVDs and a variety of illegal drugs. Adams was accused of drugging and raping a 12-year-old girl.

Under the radar

For Westerners arrested on child sex charges in South East Asia, things do not always turn out too badly. Gary Glitter got a two-and-a-half-year sentence in Vietnam for obscene acts with girls aged 10 and 12.

These are poor countries, where $100 can buy your freedom. But Ronald Adams had more to reckon with than the local police. An agent from America's Immigration and Customs Enforcement Agency (ICE) was part of the group carrying out the raid.

If Americans are coming here to do this against the Cambodians... it's our responsibility to bring that person to justice Special agent Chris Materelli

If a US citizen is caught abusing children abroad, American agents are now on hand with the specific aim of getting the suspect on a plane to stand trial back in the US.

ICE is part of the Department of Homeland Security, based in Washington, with a severe, Brooks Brothers-suited lawyer, John Morton, as its director.

"Don't think that simply by buying a plane ticket to leave the United States and going to a country with less robust investigative and prosecutorial capacities that you are going to be able to get away with it again," Morton said.

"Perfect example - the three gentlemen we brought back from Cambodia."

The "three gentlemen" were given the moniker Twisted Travellers by ICE in a heavily publicised and deliberately humiliating extradition from Cambodia 18 months ago.

All three had previous convictions for abusing small children in the US. The oldest, 75-year-old former marine Jack Sporich, now faces a sentence of 15 years for sexually abusing a number of young boys.

Cambodia's jails are full of foreign paedophiles, but for most of them a short sentence is all they have to worry about. But even that can be avoided if you have the money to pay off the police and the judge.

Image caption Agent Vansak Suos was once a conscripted boy soldier in Pol Pot's Khmer Rouge army

America was the first country to be positively pro-active about arresting and returning their child abusers to face justice. It has been joined in the past 12 months by Australia and Canada.

For US special agent Chris Materelli, it is as much about moral responsibility as law enforcement.

"If Americans are coming here to do this against the Cambodians, it's our job to try to help the Cambodians clean it up," he says. "They're our citizens, it's our responsibility to bring that person to justice."

In the seven years since the Protect Act was passed, America has brought back 85 child sex tourists to face justice in the US.

But none of this would work without a ground-breaking change in the way US agents work - not just with local police, but NGOs run by ordinary citizens.

In the tourist hot-spots of Cambodia, Action Pour Les Enfants (Action For Children, APLE) acts as the eyes and the ears of ICE in keeping surveillance on suspect Americans.

That's a common defence - that these kids are older than what they appear to be because they're Asian Gary Philips, ICE agent

Young men on motorbikes patrol the streets with video cameras supplied by the Americans. It was an APLE undercover team that came across Ronald Adams openly asking for sex with underage girls, "the younger the better".

This kind of co-operation with ordinary locals represents a massive change of attitude, almost unthinkable 30 years ago in the wake of America's bombing of Cambodia.

Cambodians are welcome within the ranks of ICE agents. Vansak Suos, once a conscripted boy soldier in Pol Pot's Khmer Rouge army, now occupies an office in the US Embassy in Phnom Penh, with a photo of himself and Bill Clinton on his desk.

Vansak's story is bleak, his brother, two sisters, and grandfather were all killed in the time of Pol Pot. He, himself, barely survived, but having done so was determined to use his life to protect other children.

Big catch

Forty-five-year-old millionaire from Florida, Kent Frank, is probably ICE's biggest catch so far. He is a serial global child sex tourist, who was caught abusing four underage girls in his hotel room in Phnom Penh.

Vansak describes how Frank tried to bribe the local police chief.

"Kent Frank just stood up and put his hand in his pocket. Then, shaking the hand with the boss. And the boss just found $100 in his hand," he says.

Frank admitted to having sex and taking photos of the girls he had been with, saying that he believed they were all over 18.

"That's a common defence, that these kids are older than what they appear to be because they're Asian," says ICE agent Gary Philips. "And if I had a nickel for every time I've heard that, I'd probably be a millionaire."

Frank tried to delete the incriminating photos on his digital camera, but at ICE's state-of-the-art cyber forensics lab back in the US, 1,600 deleted pictures were recovered. Frank is currently serving a 40-year sentence in a federal jail.

But it doesn't always end that way. After seven months on remand in a Cambodian prison, Ronald Adams was released without charge. The court decided that because his alleged victim says she was drugged, her evidence could not be relied on. He has since disappeared.

Vansak shrugs and moves on. He is, he says, proud of what he has done. Every sex offender convicted means that many more children are now safe.

This World: The Paedophile Hunters will be broadcast on BBC Two at 2200 GMT on Sunday 30 January, or catch up on BBC iPlayer.