Werner Herzog has built a reputation out of his fascination with human nature’s extremes. The German’s latest documentary, 'Into the Abyss', plumbs the nihilism of senseless killing – illegal, and state-sanctioned – through the fates of two young murderers jailed in Texas, one a lifer and the other on death row.

I’m very good at casting. I see that’s a person with whom I must speak, although I know literally nothing about them. Every single person I filmed is in the movie, with one exception - a former girlfriend of Michael Perry, and she was very dull, so I didn’t even look at the footage when editing

While fervently opposed to capital punishment, he doesn’t gloss over the brutality of the crimes or their impact on the victims. Rather than campaigning, he glories in a vision of the town of Conroe itself as a strange hinterland imbued with violence – or as he deems it, “a descent into a true American Gothic”. We met with the majestic eccentric in London to get to the bottom of his uncanny affinity with his subjects.

Dazed Digital: You interviewed Michael Perry only eight days before his scheduled execution. How did this affect the atmosphere of the interview and your feelings about it?
Werner Herzog: It was not an interview. He believed I was a reporter but I said no, I have no questions. I’m a poet. Let’s talk, and see where it takes us. You have a very limited amount of time that the prison rules dictate and a very limited amount of technical crew allowed inside, so it was obvious that it would be very, very intense. But so is every single other conversation I’m having, with people who are not in prison.

DD: Is it true you and your editor temporarily took up smoking again, as it was so stressful?
Werner Herzog: I admit it, yes. I stopped smoking about ten years ago. But in a case like this we had to rush out and hang onto a cigarette, and smoke it furiously, to be able to return.

DD: In terms of the psychological pressure, how does it compare to your other films?
Werner Herzog: Psychological pressure is not the complete story. It’s something else, it’s trying to grapple with sheer nihilism, a violent crime of utter senselessness. It’s more a philosophical question than an emotional question. So there’s quite a few facets, seeing the vigour of life entering through all pores into the film, the urgency of life that was not there but in the footage. I’ve made quite a few intense films – Grizzly Man is quite intense, Aguirre the Wrath of God is intense, but this is probably the most intense film I’ve made.

DD: The cast you’ve managed to assemble seems very fortuitous…
Werner Herzog: Not fortuitous, no. I’m very good at casting. I see that’s a person with whom I must speak, although I know literally nothing about them. Every single person I filmed is in the movie, with one exception - a former girlfriend of Michael Perry, and she was very dull, so I didn’t even look at the footage when editing. There was hardly any footage because none of the people you see I met with for more than one hour in my entire life, with the exception of Melyssa Burkett - the wife of one of the perpetrators. She was suspicious about me and wanted to meet me before, so I had dinner with her in a restaurant.

There is no research. One of the finest appearances in the film was the man who was stabbed with a screwdriver, and was illiterate. He was brought along in tow with a young woman who used to be a bartender in the town of Cut and Shoot, a neighbouring town to Conroe, because he knew the two murderers as well. I realised when he shook my hand that he had an enormous amount of calluses on his palms, and that made him very likeable immediately, from working man to working man. I had been a welder to earn money for my first films, so I immediately had some sympathy.

DD: How did you get these people to open up in such a short space of time?
Werner Herzog: You have to find the right voice instantly, and with everyone differently. You hear my voice, every single one has a different voice from behind the camera, from my side. You have to read them, you have to understand them instantly, you have to know the heart of men. In a way I always had it, but I think it’s also experience, life itself, the intense life that I have had that gives you insights.

'Into the Abyss: A Tale of Death, A Tale of Life' is out this Friday