[instrumental music playing] Argos boss Jon Rouse reckons the best defense is to do what parents have always done, to keep an eye on where your kids are playing, except now the playgrounds are online, too.

The big threat now is the online world.

That didn't exist when I was a kid.

The chances of me coming across a child sex offender when I was a kid out running around, the odds stacked against that are phenomenal.

But the chances of a child now coming across a child sex offender are exponential.

So as a parent, you should be concerned.

You should take an interest in the technology you're giving your child.

[gunshots] Russia has invaded Ukraine with dozens of people killed and thousands fleeing for safety.

Jon Rouse and the Argos team have successfully uprooted one of the most dangerous child abuse networks ever uncovered.

What we started out with was a network that was run by child sex offenders, that we had infiltrated at a, at a, a VIP level.

By the time we closed that operation, we held practically every key administrative position in the network, and those administrative positions were held and appointed to law enforcement agencies around the world.

So we moved from a child sex offender network administering a very big network of offenders to law enforcement administering a very large group of sex offenders.

You know, you can't get them all.

We got a...

We got quite a few of them, but you can't get them all, and they're on boards now still talking.

But times have changed.

We will do whatever it takes to find you.

Sometimes sending that shudder of fear and making sure that they live with the level of paranoia that they deserve is warranted.

And knowing that we are coming for you and we are hunting you and we are a much bigger network than you will ever be.

And the law is on our side, as is the court of public opinion.

We're not going away.

It's in an unknown location, somewhere, anywhere in the world.

And the final phase was to identify where the actual backups and the server was being hosted so that we could end the love zone in its tracks.

And that was essentially the mission briefing that we came up with.

After raids on offenders' properties, Argos often come across hard drives with an eerily familiar organising system.

When you have a look at the collections that these child sex offenders have, you've got this interesting insight into the way their brains think.

And some of them have just got a hard drive full of images, everything, you know, everything from bestiality, adult pornography, child exploitation material, they've got everything.

But then you come across the meticulous collectors who've got the images categorized by series by the child.

And those people are consistently looking for missing components of their series.

They're like stamp collectors.

There's a constant stream of new material being uploaded there.

And we focus all of our effort on trying to find the newest material because those children are at risk right now.

And it's not like the authorities give this power to just anyone.

I have to sit in front of the judge personally and seek the approval.

So that allows us then to do things like take over accounts, to possess and distribute child exploitation material.

We can hack, we can do a range of things under our controlled operation.

As Argos boss John Rouse knows, what works is perseverance and patience, and also a little bit of forensic brilliance.

Ultimately, if you put enough resources onto these individuals, unless they're really, really good, they do make mistakes.

And it's just a matter of looking for the mistake.

If you dig back far enough, you'll find that mistake that they made.

John's been at Argos for most of his career, but he's never forgotten what it felt like to get started investigating some of the worst crimes imaginable.

I vividly remember the phone call, actually, where they told me I was being assigned to the child abuse unit.

I was pretty shocked, actually.

I'd never had any dealings with the exploitation or abuse of kids.

I had a very young daughter at that stage, and I remember the reaction of the person who told me that, going, oh, you'll be right.

Everybody goes there.

It'll be fine.

You might have heard it called child pornography, but John would never call it that.