tonight, lisa ling takes a remarkable tour of the sin city underworld and meets the people who call the tunnels home. >>> sex, lies and russian videotape. an american diplomat supposedly caught on tape having sex by a russian spy agency that may be out to get him. the "nightline" investigation. >>> plus, helicopter heist. a daring break in at a swedish cash depot, complete with booby traps and why the return of the caper is "a sign of the times". captions paid for by abc, inc. >>> good evening, i'm terry moran. las vegas, sin city. there's no place like it, casinos, show girls, bright lights, high rollers and glitzy night life. but vegas is struggling through the recession, just like every other american city. maybe worse there and beneath that famous strip of luxury hotels lies a bizarre and dark underworld. a community, literally off the grid, connected by miles of tunnels. and for the people you are about to meet, those tunnels have become home. as "nightline" contributor lisa ling now reports. >> las vegas. it's the kind of place where a few things provoke surprise anymore. but bene

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

. >>> the michael vick scandal exposed the vicious underworld of dogfighting. of his plea bargain the pro football quarterback agreed to work with the humane society to fight back against cruelty to animals and he's not the first to try and make amends. here's abc's diana avillar with tonight's "in focus" report. >> how many y'all seen a dogfighting in your lifetime? >> reporter: sean moore and anthony picket are veterans of the chicago dogfighting scene. now together with the united states humane society they are trying to end dogfighting. starting in the classroom. >> true or false question, you can go to jail for fighting dogs? >> reporter: it's not long before michael vick comes up in conversation. >> he led a dogfight. >> you know what happened to him? >> he went to jail. and he lost time for playing in the game. >> as a former dogfightinger, i share it with michael vick. not an excuse but no one could tell me dogfighting was wrong. two, tell me it was illegal. >> i didn't even know it was illegal. >> reporter: keosha and her classmates have vivid memories