Charlene Downes should have been anonymous: ordinary, nothing special, just another schoolgirl from just another family in just another town in the north of England. There are lots of Charlenes.

She'd have turned 30 this year, had she lived; fully grown, maybe a mother, perhaps weathered, definitely traumatised, certainly battered by life. Her name wouldn’t mean anything outside her world.

The area behind Blackpool promenade, with its illuminations and glitter cheesiness, can feel like a bad trip: dark alleyways and skanky side-streets rammed with flashing lights, neon signs, arcades and takeaway shops. This is the iniquity that gobbled up Charlene in November of 2003.

Two men were tried in May of 2007 – one for murder, the other for pushing her body through a mincing machine and serving her up in kebabs, her bones crushed into tile grouting. The jury failed to reach a verdict and a re-trial was scheduled, but in April of 2008 the pair were released because of dodgy evidence. To this day, the rumour mill is working overtime.

I was the first national journalist to interview the family. Not through any great insight, but through a fluke. A glossy magazine was looking for a mother of a missing child (any mother, any child, anywhere). They wanted a feature on missing kids. It just so happened that Charlene went AWOL at the same time. Fifteen years on, with countless page leads, magazine spreads and TV appearances, the story is still cooking. It won't go away.

Karen and Bob Downes visiting their daughter's memorial. Screen shot: VICE Studios / Channel 5

It's just under 15 years since I went looking for Bob and Karen Downes, Charlene's parents. I had no idea of their door number, so I knocked on every house in the street, searching for the abandoned family of a missing schoolgirl in a forgotten town. It was December of 2003, freezing, and I'd left my coat at home. I started at number one; they lived at 109.

The Downes' living room smelled, the air was like soup and the ambiance was oppressive; I could see the windows hadn’t been opened for years. Charlene had three siblings: Emma, Becki and Robert junior. Their nana had also moved up from the West Midlands looking for a new start in the "Las Vegas of the north". I chatted to Karen and her mum, Jessie, AKA Lena. Bob Downes and his mate loomed over me, watching my every move.

Karen was getting used to speaking to men in suits in her living room, but she was understandably nervous. She showed me a picture of Charlene lolling on the sofa. The very sofa I was sitting on. I asked her if anything unusual had happened to her daughter, anything out of the ordinary, any changes in her life. She told me: "Charlene said that a gang of girls was picking on her, because she didn't have the right designer boots and trainers. Charlene had caught head lice. Since then, they had called her 'tramp' and made her feel dirty. It was all silly nonsense. Charlene was always neat and tidy. We didn't have much money, but we made sure she was nicely dressed."

She showed me the bedroom she shared with her nana. It was all exactly as Charlene had left it: her Darren Day posters smiling glibly from the walls, her hairbrush – a make-shift microphone – on the table. All so childlike, so innocent; everything as it should be.

When you interview people for a living, you know when they’re lying. But it wasn’t my place to isolate her truth, I was there to document her pain. I came away, happy to move on, never to return, or so I thought.

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A few years later, I got a call asking me if I’d heard about the kid from Blackpool who’d been groomed, murdered then chopped up and put in a kebab.

"A kebab, you say?" I asked, scratching my bald head. "Are you taking the piss?"

It was the same kid, the one with the head lice and the Darren Day posters.

Of course, I didn't believe it and no newspaper would run with it. I felt stupid asking. Even the Sunday Sport thought it was far-fetched.

A few months later, a copper told me the CPS case was indeed built on "kebabs".

Preston Crown Court heard the line at the start of the trial: the prosecutor told the jury that Charlene was one of a few young girls in Blackpool who had sex with older men who worked in fast food shops, in exchange for cigarettes and alcohol. One of these men, according to a witness, had been heard talking about having sex with Charlene, before "laughingly [saying] that she had gone into the kebabs". I was stunned, but I also knew that I might as well go home. Staff reporters and the Press Association would have it sewn up. There was no point in covering the court case.

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The stories flew off the presses and it didn’t look good the for "Doner Kebab Two".

But the jury couldn't reach a decision. They were thrown back in jail and a retrial ordered. And then it got really weird: the case collapsed and the investigation ground to halt.

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Press packs and hungry agencies loitered outside Karen’s house, tabloid nasties tapped on the living room window, badgered their neighbours in the street, shoved their arms through the letter box to steal their mail. Agency jackals toured the flesh pots and the kebab shops for follow-ups.

More and more stories came out: it was a feeding frenzy, and I soon found myself sitting in Karen’s living room, again. A reporter from The People warned Karen: "Stay away from him, he’s the biggest shark of the lot."

I don't know why I got all the stories; I just did.

The "stuff" happened, it just kept on and on. The story wouldn’t stop giving and I’m still writing, interviewing and gathering souls; a piece of me still stuck on that murky sofa in 109 Purgatory Street.

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I'd never really gotten to know Karen or Bob or any of the family. I just dashed in, got the details and the signature and dashed out – a lot, over a long period of time.

Blackpool is the "whitest" place I know, and Karen’s event magnet inevitably drew in the right-wing "head-the-balls" brigade, as well as the radical notion farmers of the broadsheet press. All really fucking tedious. While I was keen to side-step the lot, somehow, I was still in the picture. I began to get a feel for the place and the kid, but who cares what I think?

I felt haunted by it – uncharacteristically restless, even. So I went looking for the people who had something to say and something to hide. The people who knew her, who loved her, who exploited her, who cashed in on her, who sold her down the swanny.

The Murder of Charlene Downes – a VICE Studios-produced documentary, for Channel 5 – follows me on a journey to revisit the events of 2003. To look at the end game of a teenage outsider and examine how a young girl can disappear from the streets of Britain without two fucks being given by so many.

Some viewed the Downes family as complicit in Charlene's downfall, unworthy victims not deserving of our sympathy, white trash: lived by the sword, played with fire, skirted too close to the edge, etc, etc, etc. Some said she was from a scum family and she didn't matter. She wasn’t a middle class kid with erudite, professional class parents from middle England.

Really, though, Charlene was an innocent kid incapable of making an informed decision. An innocent kid with nobody looking out for her. Abusers prey on the most vulnerable, and that means forgotten latch-key kids from long lines of forgotten people.

So many people – professionals, friends, locals – will tell you the real story. What was really happening in Blackpool. But it’s easy to be clever. None of them did anything while the kid was alive. All disinterested in her life, yet fascinated by her death.

Karen was given a chance to tell the world what happened to her. She was given the opportunity and the help – by my wife, Ann, and I – to write a book and lay out the unbearable weight of losing a child, and a chance to atone for the mistakes she made and to hold her hands up, shoulder some of the blame – maybe to try to heal some wounds, keep her daughter’s memory alive, let people know her pain: a mother’s pain.

In the film, we see her reach the limit of her truth. We watch her struggle with the chain. She needs someone to blame – someone to deflect the guilt away from herself.

The facts left out of Karen’s story were the very facts that exposed her daughter to the risks that eventually claimed her. I know: I helped ghost write her book.

I have been passed bundles of reports into Charlene, but none of them amount to a hill of beans. Charlene is dead and nothing was done while the poor kid was alive. She was vulnerable, damaged, abused, kicked out of school, preyed upon by men, beaten and shouted at, let down by police, social services, her family, her neighbours, health care workers.

And journalists, of which I was one. It’s just a story to them – to me.

The tabloid news editors were thrilled with a good "meaty" yarn, as were the broadsheet opinion formers, who set about using Charlene as a case history to back up their highbrow sociological analysis of 21st century Britain – when, really, it was just another example of posh people telling the hordes on the bottom rung how to think and what to do.

The uncomfortable truth is that Charlene Downes' death makes a great story: the teenager who ended up in kebab. Before the court heard that horrendous assertion, Charlene was just another missing kid, somebody else’s drama.

I don’t know who killed her, but I know who failed her.