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A BBC Trending report about predators on YouTube prompted a reader to investigate - which led to an international tip-off that resulted in the jailing of a dangerous paedophile.

Jack was just trying to get some rest, while flicking through news stories online.

"I read your article lying in bed like most nights, waiting for sleep to find me, with my wife already asleep beside me," he wrote.

But he was kept awake by a story about predators on YouTube.

It appeared on the BBC Trending blog in August 2017, one of a series of reports last year that catalogued flaws in the internet video giant's child protection measures.

Jack, a father who lives in Australia, was particularly concerned about one aspect of the report - that people were leaving predatory and grooming comments on videos made by young teenagers and children. And in many cases, they were getting away with it. Disturbing comments were left up for weeks or months, and the people behind the accounts were escaping detection or punishment except, in some cases, an account ban.

For Jack - who has asked the BBC not to publish his real name because of concerns about his online safety - it was the start of a quest.

He began to scour YouTube to try to find obscene comments aimed at children. And to his surprise, they weren't hard to find.

"Lo and behold there were hundreds, probably thousands or tens of thousands of these videos riddled with comments," he wrote in a message to BBC Trending.

"I singled one of these [people] out, looked him up, found his Facebook profile, notified a contact."

And that was the start of a chain reaction.

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The investigation

Scott Parks is a detective sergeant with the sheriff's office in Washington County, Ohio. It's a mostly rural place in the south-eastern corner of the state, tucked up next to West Virginia. There's a lot of farmland and a few factories. Industry here, as in many parts of Ohio and the Midwestern US, has suffered over the past few decades.

"It's small-town America," Det Sgt Parks says.

Image copyright Getty Images Image caption A view of the Ohio River as it separates Washington County, Ohio from West Virginia

Det Sgt Parks is a specialist with a decade of experience in child sexual abuse cases and online crime. He says he and his team tend to get, on average, a couple of such cases a week.

His involvement in this particular case started with a stroke of luck. The suspect identified by Jack was named Kenneth Siders, and Siders happened to have a police officer on his Facebook friends list.

It was that law enforcement officer that Jack contacted out of the blue from Australia, to pass on his concerns about Siders' online activity.

The officer worked in the next county over from where Siders lived, and after getting the initial tip, he passed it to the Washington County authorities. From there, it ended up on Scott Parks' desk.

At about the same time, the sheriffs had received a separate piece of information from another member of the public. It was a second or third-hand comment about how someone had possibly seen some child abuse images on Siders' computer.

By itself it wasn't much to go on, but along with the tip from the BBC reader, it was enough evidence for Det Sgt Parks and his colleagues to start an investigation. It didn't take long for the detective to discover some hints of a very disturbing nature.

"The guy... was liking a bunch of videos that were of young girls walking around in their underwear. Sometimes they wouldn't have their shirts on," he says. "That may appear relatively innocuous, but it had that undertone. If you look at these things through a certain lens, you start to see a pattern.

"So I typed up a search warrant in light of that information for Mr Siders' residence and we executed it the next day," Det Sgt Parks says.

The arrest

Many times, when police execute a search warrant, they don't know exactly what they will find - if the suspect will be home, or if they will find evidence of a crime. With this in mind, Det Sgt Parks and his colleagues travelled to Siders' home.

"He kind of lives in a rural area, there are some trailers around and things like that. He lived in a mobile home," Det Sgt Parks recalls.

"He came to the door. Initially he had some women's clothes on and he said he wanted to change before he spoke with me and I said that was fine," he says. "He then spoke with me in my vehicle while we searched the residence."

Siders, he says, spoke "matter of factly".

"He didn't totally deny what he was doing... he didn't downplay it," Det Sgt Parks says. "He said he had an interest in looking at naked people of all different ages - he liked looking at naked girls.

"I ask him what would be the oldest nude person you would be interested in looking at and he said maybe in their thirties or forties. I asked him what the bottom end would be as far as age goes... and he said there really wasn't one."

Hear investigating officer Scott Parks on BBC Trending radio

While Det Sgt Parks spoke to the suspect in the car, it didn't take long for investigators to find evidence of serious crimes. There were abusive images on Siders' computer and mobile phone.

In the course of the investigation it also turned out that Siders' crimes did not only occur online, and he had been abusing young girls in the community. Among other crimes, he sexually abused the daughters of a friend.

In November, Siders pleaded guilty to multiple charges of illegal use of a minor in nudity oriented material, gross sexual imposition and pandering obscenity involving a minor. He was sentenced to 10 years in prison.

'Life sentence'

Aged 69 and in poor health, Siders "is probably going to spend the rest of his days in prison," Det Sgt Parks says.

The detective says he's no longer shocked by cases such as these: "I've kind of grown to get used to the fact that humans can be very unkind to one another.

"I've never heard (Siders) be remorseful about any of this. All the way through his sentencing I don't believe he ever showed an ounce of remorse," he says.

Jack, the Australian who initially tipped off the police, is astonished at the ease with which he was able to find a criminal online.

"I did this with no help over a period of 10 days. With no resources except my home internet, and a half dozen Facebook messages between myself and a police officer. About 15 minutes of my time," he wrote to Trending at the conclusion of the case.

And Det Sgt Parks is grateful.

"If more people were like the gentleman in Australia, we would catch a lot more of these guys," he says. "That's amazing and I applaud that guy. The police can't be everywhere all the time, especially on the internet."

The case shows the double-edged nature of social media - and indeed of any new communications technology. A dangerous paedophile was able to use the internet for his own purposes. But it also allowed a story to be circulated worldwide, and enabled one man to take action, by following the clues left online by the criminal himself.

Det Sgt Parks has a warning for potential predators and a plea for the rest of us.

"People should be aware that if they're going to do this, we'll be looking for you," he says.

"It's everybody's on the planet's job to take care of kids. Especially on the internet. There's just not enough police out there. It takes people - it takes everybody."

Illustrations by Katie Horwich

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