this is "nightline." >> tonight, the jihadi mindset. what turns an altar boy into an isis supporter? our reporter coming face-to-face with a young radicalized recruit. >> do you think you'll be going back to isis? >> peeling back the layers of the lure of isis. and the woman who tried to raise the alarm a decade ago. plus what the twitterverse giveth instagram can snapchat away. the 21st century nightmare for 20-somethings learning the perils of social media in the most dramatic ways imaginable. when saying i do means a whole lot of cash. is this really a billion-dollar wedding? fireworks, a $25,000 gown, and a personal serenade from j. lo. first here are the

"nightline 5." ♪ come on and do it come on let's go ♪ ♪ got to keep moving come on let's go ♪ covering. is caring. because covering heal s faster. for a bandage that stays with you and moves all day, band-aid flexible

good evening. tonight you are going to see extraordinary and in many ways surprising epcounters with young people who have been won over to the side of isis. their bloody goals, their nile istic world view, and the one

mom who tried to warn police about what was happening with her son. here's "nightline" contributor maryan that van zeller with our series "face-to-face." >> do you think you'll be going back to isis? >> my dream is still to live under islamic caliphate. >> reporter: born in belgium, raised in the catholic church, the former altar boy may not fit the profile of an isis recruit. >> sooner or later they'll make to it europe? >> i think they're already in europe. isis is not a group, it's a ideology. >> reporter: this radical ideology compelling thousands of europeans and americans to join isis, inspiring home-grown terrorists in paris, san bernardino, brussels. >> the koran says cut the heads off of the nonmuslim -- >> reporter: the attacks fuelling a smoldering fire of far-right nationalist movements. creating what some are calling a perfect breeding ground for recruitment.

>> hate feeds off hate. it's a vicious cycle. >> reporter: i traveled to europe to find out what isis recruitment actually looks like to pinpoint the moment a home grown terrorist is created. this is how i found myself in belgium just a month before last week's tragedy and face-to-face with a man who could be in jail if he lived in the united states. for providing material support to a terror group. michael delafortre was part of an early wave of europeans traveling to syria to join isis. last year he was convicted on terror charges in belgium. he only received three years' probation. >> are they islamic state fighters? >> these are my brothers in islam. >> why do you think people like yourself are joining isis? >> we have people, not only people who are uneducated, we have doctors, we have nurses. those people also leave. and because of what? because they believe there's something better than this society. >> reporter: before he traveled to syria to join isis, he fell in with a group of like-minded

fundamentalists called sharia for belgium. the organization rejects democracy and calls for the kun re to adopt the islamic system of rules and laws known as sharia. >> sharia is something every muslim has to agree with. >> stonings for adultery, the death of homosexuals? >> yes, complete shsharia. >> you believe in all of this? >> i believe in all of it. >> reporter: after the start of civil war in syria sharia for belgium became a primary recruiter of foreign fighters. he set off for syria in december 2013. >> how many people do you know from your group of friends who have joined isis? >> 60. >> 60? what happened to those 60? >> i don't know, a lot of them are -- went to paradise. >> you mean a lot of them died? >> the majority, yeah. >> reporter: in molenbeek, what's being called a jihadi capital of europe, i went to meet the mother of another young man lured by this message. >> why do you think your son

went to syria? why do you think he joined isis? >> because it was thinking that he has no place here. >> reporter: geraldine says growing up her son was a fairly typical teenager. but after he graduated, anis, whose father was moroccan are was unemployed. searching for direction he appeared to become more serious about his faith. >> he was praying five times a day. >> reporter: he was being radicalized and recruited to join isis. >> we did what we can do to stop him. >> reporter: when anis announced he was going to syria, she notified the police. the police never intervened and anis made his way to turkey and the border with syria. >> they told you they knew your son was joining isis, but they decided because he was 18 years old he was an adult, they were just going to let him go? >> yes, he can do what he wanted, we can't stop it. >> reporter: anis was killed in syria. >> i have a short message. from a friend who was there with

him. and -- he said to me, your son is dead during an attack. you must be proud of him. he was a good guy. everybody loves him. be proud of him. and nothing else. no body. nothing. >> reporter: today, geraldine blames the recruiters who convinced her son that it was his duty as a muslim to join the islamic state. >> we don't understand how they are able to change the brain. the brain of the young. to accept to do that. >> reporter: what authorities didn't count on is that some of those young men would come back. including this man standing next to anis in a photo from syria. he's abdel hamid aboud, from molenbeek, and the suspected ringleader of the paris attacks.

this 25-year-old uber driver was there that night. his first response was to help shuttle people out of the area of the attacks. but after things settled down and the identity of the attackers became known, he said another reaction. >> reporter: all of the known gunmen turned out to be european citizens. and in many ways they share the same profile he does. young muslims who are born in europe, the sons of immigrants. prime targets for isis recruitment. he insists most people here are thinking more about putting food on the table than jihad. still, high unemployment, poverty, and marginalization here makes it fertile for radicalization. the message is often spread through slick online videos. but also face-to-face. sometimes starting as simple

conversations. >> why do you think it works with some people and not with other in this why didn't it work with you? you're saying it works on some people because if you're more isolated, if you don't really have a job, they're easy prey, and they easily become radicalized? they feel like they're caught in the middle between the more radical islam that doesn't like them and disapproves of them and would like to see them dead, and french who see them as outsiders and who don't feel like they belong in france. it's these kinds of insecurities that extremist groups exploit.

something that adjouthis journa has been warning about for years. i met her in belgium where a decade ago she tried to alert authorities of the growing threat after she went undercover in molenbeek to investigate rumors of radicalization. >> i heard an imam telling in his friday sermon that people should go and join the jihad. so it was very -- it wasn't discreet. it was like it was normal. >> reporter: at the time, her investigation was largely dismissed by authorities. >> they just told me that i was too young, i just was manipulated by young people on the streets. but the question is now who? who got manipulated? >> reporter: after the brussels attacks happened i checked back in with her. >> you warned about this ten years ago, what does this mean?

>> it makes me feel very sad. because i didn't want to be right. the people, especially on the right wing, would say these events to give more reason to their racist points of view. >> reporter: after traveling extensively here, it seems there's little to bridge the divide between europe 's extremes, echoed in the u.s. they all have one thing in common -- the message to muslims from the far right is essentially the same used by islamic extremists. >> you have to listen to these young people. we have to give them a voice. >> before they become radicalized they need to feel like they have a voice and they have a place in society? >> absolutely, yes. i have to say i'm scared. not for myself but for my children. in what kind of world are they growing up? >> reporter: for "nightline," i'm marianne that van zellner paris.

>> you can see mare ree yry ann report on abcnews.com. how speending a harmless twt can bring down a world of hurt, social media gone terribly wrong. and images from the most expensive wedding ever. they even got j. lo to play. many people clean their dentures with toothpaste or plain water. and even though their dentures look clean, in reality they're not. if a denture were to be put under a microscope, we can see all the bacteria that still exists on the denture, and that bacteria multiplies very rapidly. that's why dentists recommend cleaning with polident everyday. polident's unique micro clean formula works in just 3 minutes, killing 99.99% of odor causing bacteria. for a cleaner, fresher, brighter denture every day.

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anybody who's ever glanced

at the comments section of an online article or video knows the internet can be a dark and venomous place. the people you're about to meet generated shocking blowback and had their lives dramatically altered as a result of just one tweet. here's my "nightline" coanchor juju chang. >> reporter: nicole crowther says she never saw it coming. one single action changed her life forever. >> i was receiving death threats. >> reporter: and the cause of all this hatred? a single tweet. it's the well-documented dark side of the web. the new normal for 20-somethings. as featured in the syfy series "the internet ruined my life." >> everybody wants to be internet famous. >> thousands of people are telling you, you don't deserve to live. >> reporter: for 26-year-old nicole her nightmare came wrapped in her biggest dream, as an extra on her favorite show "glee." >> i was a gleek, obsessed with the show. the episode that i was in was episode 7. as he's leaving, you'll be able

to see me, i'm wearing the creamy cardigan, long cardigan and jeans, running down the hallway. and that was it, it was half a second. >> reporter: like many "glee" addicts nicole took to twitter to speculate, mostly rumors, about the show. >> i put hypotheticals up. >> reporter: one rumor she says she heard from fellow extras turned out to be all too true. nicole sent out a tweet that wouldn't even make sense to most people. >> k is pq and ka is pk. >> did you tell anybody else? >> reporter: the cryptic letters a code, a major plot spoiler for the second season of "glee" saying character kurt would be prom queen and his bully would be prom king. >> come out. make a difference. >> i sent that tweet out. the following morning is when everything hit the fan. >> reporter: turns out a glee producer saw the tweet and responded saying, who are you to spoil something talented people have spent months to create?

hope you're qualified to do something besides work in entertainment. >> right off the bat, they hated me. to put it very clear and simple. they hated me. okay this one, who invited you back, nicole crowther, go away. are you going to be hit by a train? that would be fun. >> reporter: and the tweets only got worse. some saying she should be killed. how serious are these online threats? >> these are very serious. there is no difference between someone being threatened with physical violence, emotional violence, or dead threats on a face-to-face basis than online. >> reporter: as for her budding career in film, nicole says she was blacklisted from working as an extra. >> i got dropped from my background agency. they no longer wanted to work with me. >> reporter: five years later, she now works with her family's roofing business in sunny florida. doing, of all things, social media. more than 4,000 miles away, lee van bryans' tweets are picked up by a different audience. in 2012, the irish-born british

bartender and a close friend boarded a flight from london to their first visit to america, a lavish vacation in los angeles. weeks before he tweeted out his excitement to his roughly 1,000 followers. >> the first tweet i sent which was to my friend melissa was, are you free this week for a gossip/prep before i go destroy america? and i ended with a kiss. >> reporter: the key word, "destroy." >> basically in england, destroy means to party, to have a great time. so there was no malice behind it. >> reporter: but u.s. security officials didn't see it that way. when lee got off the plane in l.a. he says he and his friend were met by customs and border agents and held for two days. as seen here in this syfy recreation. >> there was handcuffs, we were put in a cage, we were sent to a detention center, i was put in with foreign drug dealers. >> reporter: customs and border protection confirmed to abc news

at the time that two people were taken in for secondary interviews. and deemed both inadmissible to the united states. after spending less than 48 hours on u.s. soil, leigh was sent back to the uk with his visa denied. the only way we were able to speak to him, through skype. what's your social media profile like? how seriously do you take it? >> my social media profile is very just dry, sarcastic, british humor. i mostly interact with my friends or family members. >> reporter: and as for the idea that he could actually destroy america? >> i can't even destroy my living room, let alone your country. i could probably destroy a few pairs of knickers but that's about it. >> did it ever occur to you that you could get caught up in an international terrorist dragnet? >> it never occurred to me i could get caught up in this sort of scenario where i was accused of being a terrorist. i thought of all the things in the world the worst thing that probably would ever happen to me

would be that i'd end up in a girl band. >> reporter: to any u.s. officials out there who may be listening, leigh has a message. >> i would delete my twitter account if you guys would let me back in the country. i would be the best citizen you've ever had. and what happened to me was worse than when jerry left the spice girls. so you need to do me this one little favor and let me come and be an american. >> reporter: he's making his case to come back one tweet at a time. for "nightline," i'm juju chang in new york. next, they're calling it the billion-dollar wedding. the $25,000 dress and not just your average band. sting and j. lo. ya know, viagra helps guys with erectile dysfunction get and keep an erection.

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object? behold what the russian media is calling the most expensive wedding ever. ♪ >> reporter: it's hard to ignore the irony. the woman who once sang "love don't cost a thing" performing at what their calling a billion-dollar wedding. sayid gutsarid, oxford-educated heir to a russian oil fortune, got married to a 20-year-olded bring in russia over the weekend. nobody knows the total cost but the bride said i do in a $25,000 couture gown weighing in at 25 pounds. the 600 guests entered through a walkway that could have rivaled cinderella's castle. the venue was carpeted in flowers. the entertainment? along with the aforementioned j. lo -- ♪ every breath you take >> reporter: sting sang his classic "every breath you take." and