tonight on "nightline," hunting the predators. it's an exclusive hidden camera investigation into a depraved sexual underworld. the sting under cover footage shows this predator at work. >> when i kiss her i feel like i'm kissing a statue because there's no response. just like a limp pillow. >> totally unaware he is under surveillance. and a fight to change this disturbing reality and help to save the children. a special edition of "nightline" starts right now. captions paid for by abc, inc. good evening. i'm terry moran. and tonight we're going to take a deeper look inside the disturbing world of child predators. the recent case out in california involving jaycee lee dugard and her accused predator explain what they'll go to explore their perverted desires and as dan harris discovered in stunning detail for some that pursuit means travelling thousands of miles away to a place where the child sex trade is running rampant. >> we are snaking through the streets of cam bose ya's -- c cambod cambodia's capital city. on the tail of a suspected american pedophile who has no idea that his every move is being watched. his name is harvey johnson. he's 57 years old, a failed real estate developer from arizona. here in cambodia he's been teaching english out of his home which has given him plenty of opportunity to get close to children. investigators from a nonprofit group called aple first noticed johnson in october of 2007, when they say he was behaving suspiciously with children in public. they have been tracking him day and night for the last two years. aple used an undercover spy agent to befriend johnson. in this hidden camera video, johnson is allegedly selling the agent child pornography. the agent recorded hours of conversation in which he says johnson speaks freely about molesting young girls. >> but it was very slow. >> investigators now tell us that an arrest may be coming very soon. >> show me where the camera is. >> the camera -- this is the camera. yeah. >> looks good. >> and they have agreed to give us extraordinary access to the final days of their efforts to take down harvey johnson. as you are about to see, these guys have this surveillance thing down to a science. they have harvey johnson entirely surrounded. >> yeah. >> aple agent take us to -- takes us to johnson's home. >> they're telling me now they're forcing into -- four children into harvey johnson's ohouse. >> four children? four little girls? >> this area -- for the investigator? >> on johnson's street they have agents staked out at strategic locations posing as motor bike taxi drivers. this is an aple agent posing as a vendor of cold drinks. they even had agents staked out in the house next door to johnson. one of the agents points out these three girls who he says are johnson's students and his victims. they appear to have recently left johnson's house. then to our surprise we spot johnson himself sitting at an outdoor restaurant. >> we're going to go to the same restaurant. >> as we go in to take a closer look, he strikes up a conversation. >> a couple weeks? >> a couple weeks. yeah. >> enjoying all the -- >> exactly. exactly. >> he gives us pointers on where to stay. >> it's a nicer location, you get to -- the interesting places like martinis and -- >> martinis is a notorious nightclub, reputedly filled with underage prostitutes. >> what's your name? >> harvey. >> he gives us his phone number and we leave before he gets suspicious. >> let's get out of here. >> as investigators make their final preparations for the raid on harvey johnson, we go out to get a fuller picture of the profoundly depraved sexual underworld here in cambodia. pedophiles from america and all over the world come here because the people are poor and the police are often corrupt. watch what happens when we roll in to this neighborhood, known as a place where children are sold for sex. how old is this girl? >> 14. >> she's 14? >> yeah. >> it's really easy to do this. >> yes. >> two? >> 13 and 14. >> 13 and 14? >> the cops pull up. but instead of arresting us, they open our back door and try to push two girls inside. the police are here and they're pushing the girls in the car? so you can have -- you can sell a 14 or 15-year-old girl and the police don't stop you? >> no, no. >> it's okay? >> yeah. >> it's three days before the raid on harvey johnson and we attend the trial of this man. sir, the charges against you true? excuse me, sir? sir, are the charges against you true? did you abuse those kids? his name is michael dodd, a registered sex offender in florida who even though he was still on parole somehow managed to leave the u.s. and move to cambodia. now, dodd is minutes away from standing trial along with the woman to his right. they are accused of arranging a marriage between dodd and the woman's 14-year-old daughter. >> can i ask her a question? >> in this kwlund cover video, aple's spy agent translates while dodd complains to the girl's mother that her daughter is being insufficiently affectionate with him. despite how much money he is giving to the family. >> when i kiss her, it's like i'm kissing a statue, like a limp pillow. the mom says don't mind her because she's young. she's not like an older person. and so she see -- what she sees on tv -- [ inaudible ]. >> after the trial, dodd is being taken back to prison to await his verdict, he speaks to us. the allegation against you is that you essentially took advantage of a vulnerable family, paying them off to have access to the younger daughter. >> right. >> you're saying there's nothing to it? >> no. i loved her, i was crazy about her. >> how can you be in love with her? you're roughly 60 years old, she doesn't speak your language, she's very young. >> well, look at this. our previous generation before we were born, before they made the age limit, there wasn't such -- i'm sorry. >> hi. my name is dan. outside the courthouse, we meet dodd's victim. do you think michael dodd behaved inappropriately with you? >> improper. wrong. >> did he sexually abuse you? >> yes. >> yes? we watch as the girl is completely shunned by members of her own family who blame her for getting her mother in trouble. only her younger brother, too young to understand, comes over to give her a hug. after several days of following the harvey johnson investigation, we are called and told that something big is about to happen. >> first thing sunday morning we have been called to the house right next door to harvey's house. the arrest we're told is imminent. >> agents from aple and ice have gathered to wait. >> he's just left his house. he's walking this way. he's having breakfast at a restaurant just down the street which is the same place we saw him a couple of days ago. an undercover police officer rolls up. police are starting to close in. the police officer on the walkie talkie. >> suddenly, we are racing to see a raid two years in the making. but those days came and went, and the cigarettes remained. but today's a new day. and a few simple steps can make a real difference in your next quit... things like starting with a plan to quit smoking... getting support... and talking to your doctor about how prescription treatments can help you. talk to your doctor about prescription treatment options. and make this time, your time. thanks to this quick home penergy check-up from bge.house feels like i'm at a day spa. 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[sigh] ah... the efficient life is the good life. it is a far away country children are a much easier target for pedophiles, but cambodian authorities with help from the united states and from nongovernmental organizations, they are now turning up the heat in an operation called twisted traveller. their goal -- crack down on suspected sex tourists abroad an in some cases bring them home to face american justice. more now from dan harris. >> we are racing down a narrow back alley in cambodia as the cops move in to arrest harvey johnson. suspected of abusing little girls here for nearly two years. johnson looks surprised, but also surprisingly calm. harvey, i'm dan harris from abc news. the police say that you have been abusing girls here in cambodia for the past couple of years. >> i have only been here two years. >> yeah. >> i have no idea -- >> they have been following you for two years. a group called aple which is an ngo which investigates sex, they have been following you for two years and they say that you have been abusing girls and that they have proof of that. >> i don't know -- >> there's no truth to that? >> no. >> you have not abused any girls in your time here at all? >> no. >> what about the pictures of you with girls coming and going from your house? very young. >> i'm a teach. coming in and out all the time. >> they also have you on an audiotape of you saying that you had inserted your finger into one of the girls. >> i don't know what they're talking about. >> but it's your voice. >> i don't know what they're talking about. >> the cops walk harvey down the street to their awaiting vehicles as a crowd gathered. did you have any idea they were following you for two years? >> no. >> you had no idea? >> no. >> they have been on you for pretty much every minute of two years. >> i don't know what you're talking about. >> they had agents staked out in the house next to yours. they have been following you. >> no. >> does it surprise you? >> shocked, yeah. >> i know a lot of people -- i teach. i teach older people. i teach children. >> so you're confident this will turn into nothing? >> sure. for sure. >> harvey is taken down to the station. but this story is far from over. now the cops have to make the case stick, which is why the search they'll conduct the next morning is crucial. neither should you. thank you claritin-d. 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>> there were children living here. do you have porn at your house? >> what about the cameras in the bedroom? video cameras. >> well, they're not mine. >> they're not yours? >> no. they're the man who owns the house. there were a lot of cameras. >> back at the police station, harvey johnson's alleged victims, many in ponytails and pajamas have been called to give statements. one little girl's mother was totally unaware of the alleged abuse until now. when i found out she says, i wanted to die. but getting parents and children to actually testify in court can be tricky. which is one reason why this case could still crumble. in part because parents are sometimes complicit in the abuse of their children. what's that? and as we learn, it can be astonishing easy to buy a child from her mother. we meet this 15-year-old girl selling water on the street. she trotzes us to -- she introduce us to her mother and in broad daylight her mother says she is willing to make a deal. so you're saying that if i wanted to marry your daughter that would be okay? >> okay. okay. all it takes is one more visit to put the finishing touches on the negotiations. >> can i get a sense of how much that would be? $200 or $300 a month? has her daughter been with any men before me? >> no, no. we don't traffic -- >> if i don't trust, i can take her to the hospital. >> for medical examination. >> how can a mother so casually agree to sell her child into sexual servitude? the answer may lie in part in history. today's cambodian parents were raised during the worst genocide of the century during which two million children died and were encouraged to spy on and execute their parents and some believe this has left a moral vacuum. now there's a coordinated effort involving both cambodians and americans to bust pedophiles and heal their young victims. victims like this girl named bella. did they force you to have sex every day? >> yes. >> every day? for years? bella when she was a sex slave. video taken by an evangelical group called the international justice mission. the group later rescued bella and brought her to live here at this shelter where she can finally be a child again. >> because i can study and i can get love. and i can have -- >> there's now more help for victims, and increasingly a crackdown on the predators. many of these men are being held here. so this is the largest prison in cambodia? it is not a safe place for children to -- pretty violent inside here. we are some of the first journalists the cambodian government has ever allowed inside here. this is the complaint against eric -- erik peeters who's in the next room here. accused of abusing several boys and they testified that he touched them inappropriately and also sodomized them. erik, hi, i'm dan harris, i'm from abc news. can i ask you a quick question? >> it depends -- >> we want to talk about the charges against you. >> sorry, i can't speak about that. >> there are three boys who said you abused them. >> i can't speak -- >> is it true? >> american law enforcement officials believe the charges. just days after we meet him, erik peeters and two others suspected sex tourists are brought back to america by immigration and customs enforcement agents to stand trial. agents are also taking a look at the evidence gathered in the harvey johnson case, but as of yet, only one girl is willing to testify. if that doesn't change, johnson could be out of prison and may be back on the streets of cambodia or america in less than three years. for "nightline," this is dan harris in cambodia. >> since our report was shot, michael dodd, the sex offender from florida who dan interviewed in the jail there was sentenced to ten years in prison for his sexual offenses. as our team reported there are many organizations out there fighting against child sexual exploitation. you can find several ways that you can help the children on the "nightline" page at abcnews.com. our thanks to dan harris and his team for that extraordinary report. when we come back, the challenge of prosecuting american pred -- pedophiles abroad. that's the subject of "closing argument."