We focus on the part of the internet that most people don't know about.

It's called the dark web.

Undercover in the furthest corners of the dark web,

US special agents are on a mission to locate and rescue children from abuse.

Move in now.

Police!

From the BBC World Service, World of Secrets,

the darkest web follows their shocking investigations.

Listen on BBC.com or wherever you get to your BBC podcasts.

Before we begin, this episode refers to child sexual abuse.

It also contains strong language.

For 40 years, a little boy called Vishal Marotra, who was abducted and murdered in

1981, had largely been forgotten, except by his family and those who knew and loved him.

I was told by the police that they had found the remains, and I broke down completely.

They turned on the TV, and there it was, it was on the news.

And that's how I learned that my brother was dead.

Our investigations raised questions about a group of paedophiles based around a school in Sussex, close to where

Vishal's body was found. One of the men had a document in his possession that he'd named

Vishal but couldn't explain why. Sussex police knew about these men, but barely investigated

them. My personal view on this was that this little boy deserve better

than just knocking on someone's door and basically saying,

here, mate, did you murder someone back in the 80s?

...