The first time Kubiiki Pride used Backpage, America’s largest classified website, was to buy a fridge. The second time she sold some clothes. The third time she was looking for her 13-year-old daughter.

The family had spent nine frantic months looking for MA, posting flyers, launching public appeals and scouring the streets. It took Kubiiki less than five minutes to find her on Backpage. “We were so desperate we were trying everything, but when my husband said check Backpage I was confused because I thought it was a site where you sold stuff you didn’t want any more. It never occurred to me that children were being bought and sold, too.”

Kubiiki found the site and clicked on the adult section. “It took a minute for the page to load, but immediately the third link down from the top just caught my eye,” she says. “It was covered in hearts and these little flower pictures. It looked like something a kid would like, so I clicked on it and there was my baby.”

Initially Kubiiki was so flooded with relief at finding her daughter that she didn’t register what she was seeing. “At first I didn’t see the nakedness or what she was wearing or the poses she was in, but then it began to sink in, what the ad was for, and everything just fell apart.”

The Prides’ journey into the darkness of America’s domestic sex-trafficking industry had started the previous summer with an everyday act of teenage defiance. Kubiiki had told her daughter MA she was too young to attend an end-of-school party. Later that night MA sneaked out to join her friends, but found herself alone and without a ride home. A woman passing by offered help. “And that,” says Kubiiki, “was the start of my baby’s descent into hell.”

MA never made it home. Instead she was taken to a house, raped, beaten and fed drugs. “My 13-year-old was starved, had her head shaved, was abused and then, when her spirit was broken and she was addicted to the drugs she’d been given, they sold her on Backpage like she was a used car,” says Kubiiki, her voice cracking down the phone line from her home in Atlanta, Georgia. “When we got her home, a piece of her soul had gone forever.”

The trafficker was caught and given five years in jail, but the explicit photos of MA remained online. “I called Backpage dozens of times asking them to take down those photos, that my daughter was just a child and that what had been done to her was a crime,” says Kubiiki. “They refused and said if I didn’t pay for it, they couldn’t take it down. In the end they just stopped returning my calls.”

Kubiiki’s anger at Backpage grew and grew. “Here was my child, destroyed and changed forever by what she’d gone through. Anyone could see from the pictures in the ad she was just a child, yet they allowed her to be bought and sold in this public marketplace and Backpage was making money off this abuse? I talked to MA and we said: ‘Oh no, this has to stop.’”

In 2010, Kubiiki and MA sued Backpage, arguing that the site was facilitating child sex trafficking. What they didn’t know at the time was that their lawsuit would be the first spark in an epic seven-year legal assault on the website, that it would pitch child trafficking victims against some of the world’s largest tech companies in what has been described as nothing less than the battle for the soul of the internet.

To really understand what happened, it’s important to chart how Backpage went from a feisty start-up to one of the world’s largest prostitution hubs.

In 2004, Backpage was launched by the iconic libertarian publishing house New Times Media (later to become Village Voice Media) on a wave of investment and optimism in the commercial potential of the internet.

The men behind Backpage – New Times Media founders Jim Larkin and publisher Michael Lacey – are to many the heroes and architects of the alternative newsweeklies movement, newspaper bad boys who championed subversion of the establishment and ushered in one of the most glorious eras of American journalism. They founded scores of independent newsweeklies in the 70s and 80s. They grew their first, the Phoenix New Times, into a national media company with a portfolio including the Village Voice in 2005.

Along the way, Lacey and Larkin grew their reputation as mavericks. Lacey had his knuckles tattooed with the word “holdfast”. In 2004, a run-in with a Maricopa County Sheriff Joe Arpaio resulted in the subsequent wrongful arrest of Larkin and Lacey in 2007 after their Phoenix paper printed details of his real-estate dealings. In 2005, in a rare interview with New York Magazine, Lacey said: “As a journalist, if you don’t get up in the morning and say, ‘Fuck you’ to someone,’ why even do it?”

New Times Media launched Backpage as an online advertising business that would keep their journalist endeavours afloat. The site included adult listings that Village Voice Media defended as being in line with its libertarian heritage. The ads also turned Backpage into a multi-million dollar commercial powerhouse and made Larkin, Lacey and Backpage CEO Carl Ferrer, very, very rich.

By 2011, a breakdown of Backpage’s weekly ad revenues put to bed any pretence that Backpage was anything but an escort service masquerading as a classifieds business – more than 90% of its weekly revenues came from this section alone.

The most cursory browse of Backpage’s UK site – it is now operational in more than 96 countries – makes this abundantly clear. Many of the sections listing cars or jobs have one or two listings per day. The escort and dating pages have hundreds, page after page of ads decorated with hearts and hot pink lips emojis and shots of half-naked female torsos selling escort services, massages and good times.

For Mary Mazzio, an award-winning documentary maker who has spent the past two years charting the battle against Backpage for her film I Am Jane Doe, the crucial turning point came when the money got serious. In 2012, Lacey, Larkin and Ferrer ditched the newspaper business and went solo with Backpage – reportedly pocketing $10m bonuses two years later.

“I certainly don’t think anyone at New Times intended for the website to become what it has become,” says Mazzio. Almost immediately after launching, reports of child trafficking among Backpage’s sex ads had started ringing alarm bells. “At first there were clear signs of good faith – they removed full-frontal nudity, hired moderators. But the thing that shocked me most about making this film was that those guys who ran Backpage, back in the day they were rabble-raising libertarians, yet, at some point, my view is that maybe the money became so outrageously intoxicating, perhaps there was this notion that the sale of children was simply collateral damage.”

Over the past decade the enormous revenue streams created by the voracious appetite for online sex ads has thrown anti-trafficking campaigners into a state of acute alarm.

“The scale of child sexual exploitation is not something many people are willing or able to accept,” says Yiota Souras, senior vice-president at the National Center for Missing and Exploited Children (NCMEC). Some campaigners believe that up to 100,000 children like MA are exploited for profit across the country every year.

“What we do know for certain is that, since 2010, the number of reports of suspected sex trafficking has gone off the chart – we registered an 846% increase between 2010-2014 and this number is growing every year,” says Souras. “And we believe a large driver of this has been the increased use of the internet in the buying and selling of children.”

Souras says the unfettered and largely unregulated growth of the internet has been a gift for traffickers. Online classified websites, such as Backpage, have provided a cheap and relatively risk-free platform through which to conduct their business, with traffickers scattering children among the thousands of ads for private massages or escort services.

“All a pimp needs is a classified website to post ads and a cell phone. All the client needs is an internet connection,” says Souras.

She laughs at Backpage’s argument that by screening ads for signs of child trafficking and reporting potential illegal activity to the authorities, online classified sites carrying adult listings are key players in the fight against online trafficking. “Let’s be clear about what these ads are about. By their own admission, Backpage edited approximately 80% of adult ads,” she says. “Even with this being the case, no one looking at the adult ads or dating section of Backpage would have any doubt that many of these ads relate to potentially illegal activity or exploitative content.”

Nobody has a clear idea of how many children have been sold on Backpage but, currently, 73% of child sex trafficking reports NCMEC receives from the public relate to Backpage ads. NCMEC’s early collaborative relationship with Backpage soured when, Souras said, it became clear the site was using NCMEC as good PR but failing to implement adequate checks and balances that the centre believed needed to be put in place to protect vulnerable children.

“They weren’t willing to invest in what we believed were comprehensive measures to protect children,” she says. “They were far more focused on hiring a legal team to ensure that their revenue streams could continue.”

Mazzio’s documentary forensically timelines the legal assault waged against Backpage, first by Kubiiki and MA and then by other families along with state prosecutors and law enforcement officers. Her film also charts the astonishment and dismay as one by one their lawsuits bit the dust.

“They just kept on winning,” says Brad Myles, director of anti-trafficking group Polaris. Judge after judge accepted that Backpage was not accountable under US law for the child trafficking occurring on its website. Backpage was, according to the courts, no different from any other web publisher provided immunity for content posted by third parties under the 1996 Communications and Decency Act, where section 230 had been included to ensure that the burgeoning tech industry was not crushed by litigation. It has also emerged that not-for-profit special interest groups funded by companies including Google have supported Backpage’s legal battles and provided expert briefs in support of the site.

“The most disheartening indication of our judiciary’s legal priorities,” says Myles, “was the fact that judges would do nothing to hold a website that was profiting from the sale of children accountable to preserve the legal immunity of the billion-dollar tech industry.”

Kubiiki and MA were devastated by the judge’s decision not to let their case against Backpage go to trial. “These are children who are being raped, yet the whole debate around Backpage has become about the rights of internet companies to not get sued?” says Kubiiki.

Yet, as Eric Goldman, professor at Santa Clara University School of Law in California and the co-director of the High Tech Law Institute, points out, the judiciary was just implementing the law. “It is crucial to understand that, under the law, if an ad comes from a third party, a website is not liable for publishing it,” he says. “It doesn’t matter if they profited from it or even if they suspect it is illegal.”

Goldman also points out the civil cases brought against Backpage by families seeking damages for the exploitation of their children, are a drop in the ocean of lawsuits engulfing Backpage over the past seven years. Many of the state and federal litigations launched against Backpage are targeting the website for all of its online sex ads, not just the cases of child trafficking that occur on its site

“I reject this concept that it is child trafficking victims versus the tech industry,” says Goldman. “My question is that if the goal of this litigation is to benefit the victims of sex trafficking, is this really the best way to do this? Will destroying Backpage stop other children being exploited online? For me, this is not about the legitimacy of online prostitution or advertising, it is that Backpage is the canary in the coalmine for section 230.

“Litigation resulting from a change to section 230,” he continues, “would be pocket change for the big tech giants. But it’s about the hundreds of other companies doing amazing things that make us happier, healthier and wealthier, and defending an assault on the freedoms of the online space. And these are values worth fighting for.”

Regardless of which side you come down on, it looks as if the net could be closing around Backpage. When Carl Ferrer failed to answer a subpoena to appear before a Senate subcommittee in 2016 investigating child trafficking, the Senate’s response was to launch a full-blown investigation into the company. One of the closing scenes in Mazzio’s documentary is the moment when Larkin, Lacey and Ferrer are forced to appear before the subcommittee in January this year.

Earlier that day Backpage had finally closed its adult services listings. “Today, the censors prevailed,” wrote Lacey and Larkin in a statement. “The shutdown of Backpage’s adult classified advertising is an assault on the First Amendment. We maintain hope for a more robust and unbowed internet in the future.”

Court footage catches the Backpage executives staring at senators, truculent and unbowed they yawn and look conspicuously at their watches before refusing to answer any questions. They cite both their First and Fifth Amendment rights while the Senate subcommittee detail the investigation findings which concluded Backpage knowingly and deliberately facilitated child trafficking for profit.

The report said that instead of working to prevent child exploitation, Backpage was focused on getting as many ads posted as possible. It instructed moderators to edit ads and strip out the code words used by pimps to indicate that the person in the ad was a child. Words such as “Lolita”, “fresh” and “amber alert” – police code word for a missing child – were edited out and the ads posted. In one subpoenaed email believed to be from Backpage management, moderators were instructed: “If in doubt about underage: the process for now should be to accept the ad…”

Backpage executives are now facing fresh criminal charges and a possible grand jury investigation in Arizona. Last month, the first civil case brought by the family of a trafficked child – JS – was also allowed to go to trial.

“It feels like finally the veil has been lifted and the idea that these people are crusaders of free speech has been blown away,” says Nacole Smith whose daughter JS was trafficked in 2011. “In less than 36 hours, my daughter went from being a 15-year-old all-American kid to being sold for sex on that website,” says Nacole. Just hours after JS left Nacole a note saying she was going to “find herself”, she met another runaway girl on the street who introduced her to a pimp. He beat and raped her and then advertised her as an escort on Backpage. A month after JS went missing she called home to wish Nacole a happy birthday.

“She was crying, saying: ‘You don’t want me, I’m broken, I’m a bad person,’” says Nacole. “To hear your own daughter say those things when all you want is for her to come back to you is beyond devastating.”

To Nacole, it is the right of the children to be heard that is the thing most worth fighting for.

“For me, the biggest tragedy is that for seven years there has been all this debate about free speech and First Amendment rights. And the basic fact that these are children who are being raped and sold on a public website somehow got pushed to the background. What happened to the rights of my child?” asks Nacole, fury in her voice. “What if this was your daughter? How would you feel if this happened to you?”

Some names have been changed. The documentary I am Jane Doe by Mary Mazzio is on Netflix