DETROIT — After nine men lured hundreds of teenage girls nationwide onto the dark web and persuaded them to strip, masturbate and perform illicit sexual acts on a webcam, many parents wonder how the predators were able to find their kids.

The case ended last week with all of the defendants being sentenced to decades in prison, including a married father of two from New York who masterminded and ran the operation. He got 40 years.

Here is how these predators, known as the "Bored Group," pulled it off, according to the FBI, prosecutors and the victims.

The men pretended to be teenage boys. They used fake profiles and stolen pictures of teens, then scoured popular social media sites looking for possible victims.

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Their hunting grounds included Gifyo, Periscope, YouNow and MyLOL.com, which describes itself as "the No. 1 teen dating site in the U.S., Australia, U.K. and Canada."

MyLOL was the group’s primary hunting ground, where the predators would comment on an old image or video a teen girl had posted to stand out from users who commented on newer images. If the girl responded to the comment, she would get an invitation to a chat room where no one policed their activity.

Each member of the group had a role.

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The "hunters" sought out girls on social-media sites and lured them to the chat rooms. Once there, the "talkers" took over, persuading girls to undress and engage in sexual activity by talking to them about a variety of subjects, like school, family, sports and sex.

The "talkers" often spent considerable time building a rapport with the girls and earning their trust, hoping the attention and compliments would lead the girls to engage in sexual activity on a webcam.

The group used a variety of manipulative techniques to get girls to undress or masturbate on camera:

• Dares. They challenged the minors to engage in certain behavior that started with innocuous things that evolved to removing clothing and showing their naked bodies and, ultimately, to engaging in sex acts.

• Polls. The group conducted polls to subtly manipulate the victim into specific activities.

The polls began as votes about which members believed a girl was pretty, looked cute or had nice eyes. Like the dares, the polls then graduated into votes about whether the victim should remove items of clothing, masturbate or engage in other activity.

• Competitions. The group sometimes would pit one minor girl against another in the chat room and give points to the girl who did the most daring things.

For example, the men would have two girls get on a web camera in one chat room and give them points for taking off certain items of clothing and engaging in sexual activity. Taking off a bra was worth 10 points; showing your breasts or genitals was worth 20 points.

The girls could go from “Level One” to “Level Two” if they obtained enough points, then to “Level Three,” and so on.

For unknown reasons, the group typically included the word “bored” in the title of their chat rooms, such as justsoboared, borednstuff, and boredascanbe — hence the name “Bored Group.”

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After the "talkers" and "hunters" got the girls into the chat rooms and earned their trust, the "loopers" stepped in.

They were used to entice the girls into engaging in sexual activity by playing previously recorded videos of teen boys performing sex acts in a chat room. The "loopers" pretended to be the teenage boys in the video, which they used to persuade the girls to do the same things.

The group even had a plan for vulnerable victims. If a girl was suicidal or revealed that she was cutting herself, the group held a "trust building session" that involved sensitive chats about life and the girl's worth.

Sex was not discussed in these sessions. But the men even persuaded some girls to cut themselves while they watched.

The group also was careful not to get caught.

For example, the group’s so-called "hunt strategy" noted that commenting on a sexually suggestive image or video may alert the victim to the true interest of the group. Therefore, the group recommended commenting on more benign images or videos to hide the real intent.

Additionally, by commenting on an older, nonsexual image or video of the girl, the group hoped to avoid what it called “heroes.” Heroes are fellow social-media users who alert girls to the sexually exploitative nature of the group, thereby thwarting their scheme.

The group kept close track of the girls, including their names, links to their social media accounts, and names of the chat rooms they visited that the men ran. The chat rooms were broken down by names:

“Camping rooms” were where members remained logged into a room in case a victim returned.

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“Regular” rooms were for new victims or girls that appeared at least once a week.

“Hero alerts” warned the group members about Internet users who had told the victims that the group was not made up of teenagers.

The group members also secretly communicated with one another in a separate chat room where they talked about the girls behind their backs to maximize the likelihood of exploitation. For example, the group praised one girl online for engaging in daring acts — she made 60 sexually explicit videos — then made fun of her behind her back for being so easy to manipulate.

"They hunted girls. They lied to girls. They manipulated girls. ... And they did so repeatedly, for years," Assistant U.S. attorneys April Russo and Kevin Mulcahy argued in court documents. "This group did not invent the sexual exploitation of children, but they may have perfected it."

However, the schemers eventually would get caught.

In 2017, one of the members linked the group to an online news article about the arrest of an unrelated online predator who had frequented the same website that they had. Worried about their own potential arrests, several members of the Bored Group stopped coming to the website and no longer appeared in the group chat.

The group didn't know the FBI already was onto them.

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For the victims, who ranged in age from 8 to 17, the arrests and convictions brought closure. But the mental scars still exist.

"I am a 20-year-old girl standing here today, facing the monsters that destroyed my childhood due to child exploitation," a New Orleans woman, who was lured into the scheme when she was 16, said at the sentencing hearing last week.

Like several other victims, whose names are not being made available because they are victims of sex crimes, she said the internet was her escape from depression and loneliness. The kids at school ignored them, but the predators did not.

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"I enjoyed having 'friends' to talk to every day. They were always there no matter what time of day," the New Orleans victim said in court.

An online friendship grew. Flirting went back and forth. And the girl used her webcam as the men captured the acts on video.

Then came the blackmail.

The men whom she thought were boys threatened to out her, come to her house and hurt her and her family if she didn't produce more sex videos, she said. So she did what they asked out of fear over and over again.

What followed were suicide attempts, hospitalizations and self-harming.

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"I know they knew I was hurting because they would watch me cry and some would even ask me to self-harm while they watched," she said, noting the nightmare still lingers. "Thinking back to those days causes me to cry myself to sleep, wondering when the monsters will stop haunting me."

The ringleader of the group, Christian Maire, 40, of Binghamton, New York, sobbed in court, saying he was sorry and remorseful, and pleaded with the judge to give him a shot at redemption. U.S. District Judge Stephen Murphy spared him life in prison, which is what prosecutors argued for, but locked him up for 40 years.

The others got similar sentences:

Michal Figura, 36, of Swarthmore, Pennsylvania, sentenced to 31¼ years.

36, of Swarthmore, Pennsylvania, sentenced to 31¼ years. Jonathan Negroni Rodriguez, 37, of West Hollywood, California, sentenced to 35 years.

37, of West Hollywood, California, sentenced to 35 years. Odell Ortega, 37, of Miami, sentenced to 37½ years.

37, of Miami, sentenced to 37½ years. Arthur Simpatico, 47, of Mississauga, Ontario, Canada, sentenced to 38 years.

47, of Mississauga, Ontario, Canada, sentenced to 38 years. Brett Jonathan Sinta, 36, of Hickory, North Carolina, sentenced to 30½ years.

36, of Hickory, North Carolina, sentenced to 30½ years. Daniel Walton, 34, of Saginaw, Texas, sentenced to 30½ years.

34, of Saginaw, Texas, sentenced to 30½ years. Caleb Young, 38, of Cuyahoga Falls, Ohio, sentenced to 30 years.

Follow Tresa Baldas on Twitter: @Tbaldas

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