It starts with a tip-off.

There were a number of red flags that made it suspicious.

It's the late '80s, and Special Agent Dennis Bass is settling in for his first day in a new job. It was meant to be the start of a quieter life. No more late-night drug busts. But then he gets a phone call, a warning about a shipment of potentially lethal chemicals. Heading to a secret destination.

We got a sample out before it left Baltimore and sent it to a lab.

Says Special Agent Bass follows the lead.

I said, If we just seize it, we have nothing.

He sets up a sting operation that uncovers more than he ever bargaining for, a global plot helping fuel a war.

When mixed on a one-on-one basis with hydrochloric acid, it becomes mustard gas.

And he said it was a chemical bomb. And a suspect, the Gasman. He loved being this evil entrepreneur. For decades, Special Agent Dennis Bass has been locked in a global game of cat and mouse with one man.

I said, Listen, you'll be looking over your shoulder for the rest of your life.

A man who's still on the run today. But this story is not about my hunt to track this fugitive down. Hello, Mr. Walischeck. Hello, this is Chloe from London. That's the thing. He's hiding in plain sight.

Fbi and the Americans are stupid. They're stupid.

It's about a sharp dresser with a gold chain, an enabler who helped a regime create a chemical weapons program. Individuals like that are extremely dangerous.

If he had hung himself, I wouldn't have lost a wink of sleep, believe me.

But whose crimes appear to have simply drifted away right under everyone's noses. Forget this fucking human rights. I hate it.

There is no human rights.

I know it does want to look at them and I would Look what you done to me. Now, so many decades later, could justice finally be catching up with the Gasman? So are you happy to start the interview? Job.

I can tell you a story.

I'm Chloe Hajimothé. This is a new six-part series from Tortus, The first two episodes will be available to listen on the 28th of May, with episodes released weekly after that. Follow the feed to make sure you don't miss an episode.