Maverick German director Werner Herzog is unable to attend the Berlinale screening of his 3D film Cave Of Forgotten Dreams this year because he’s in a “tense” period of shooting for a new documentary about death row in the US.

“I am doing a film on death row inmates who are waiting for execution,” Herzog explained to Screen in a phone interview from Houston, Texas, on Sunday. “Of course, it fascinates me to look into deep abysses of the human soul. Left and right, wherever you look, there is an abyss.”

Herzog was president of the Berlinale international jury last year, and he had been due in town this year for the out-of-competition special screening of the highly acclaimed Cave, which is being sold here by Visit Films. The 3D feature doc, shot inside the Chauvet caves of Southern France, explores the oldest known pictorial representations of humankind.

He says the 3D technology was integral to the project. “It was imperative,” he declares. “Since my film in the cave may be the only one ever permitted to be shot there because the climate is so delicate, you had to bring the audience into the cave itself.”

Herzog said the new film continues themes he explored in Cave. “It is in a way not dissimilar to what I have done in Cave Of Forgotten Dreams, [where] I am looking, historically speaking, into an abyss of 35,000 years.”

Herzog said he was actually shooting in prison this week. “It is very, very tense.” To arrange his interviews, Herzog and his team have had to negotiate with lawyers and prison wardens — and convince the prisoners themselves to appear on camera.

Herzog has five subjects — four men and one woman. All are in Texas, apart from one in Florida. The German director claims he is completely honest with the prisoners about his intentions. “I am a complete straight-shooter. You have to be, because they would smell the dead rat miles away.”

Herzog does not advocate capital punishment, but insists the film is not a crusading doc. “I am not in the business of guilt or innocence. My focus is elsewhere.” He is promising a pared-down approach with little music and less voiceover than in his recent docs.

The feature-length doc is being made for Investigation Discovery. Herzog and his team are in talks with TV stations (including Channel 4 and Arte) to board the project.

His work means he was not able to attend the Berlinale. “All of a sudden, there was a window of opportunity. I had the dilemma — to go to the Berlinale to celebrate Cave Of Forgotten Dreams or make a film that for me is quite important. I made the choice — I am going to work and not celebrate.

Once Death Row is done, Herzog will be in London in March to teach at his Rogue Film School. Meanwhile, he is also preparing a “big feature film in the desert”. He will not disclose much because, he says, “it’s not financed yet”, but it is likely to shoot in the Arabian desert.

Herzog clings to his creed that film-making should aim to reveal “ecstatic truth”. “Facts do not illuminate,” he declares. “I am looking for something where you look deep into the human soul — something you can only experience almost like a religious ecstasy. Those are the rare moments I am after.”