After appearing on screen with neo-Nazis, violent prisoners, drug addicts and Jimmy Savile, Louis Theroux says he doesn’t shy away from “the troubling side of life”.

But for his latest project, the documentary maker has stepped away from the camera to delve into one of the UK’s most notorious murder cases.

Jeremy Bamber has spent more than three decades in jail after being convicted of fatally shooting his adoptive parents Nevill and June, his sister Sheila Caffell and her six-year-old twin sons, Daniel and Nicholas, in 1985.

He has always protested his innocence and insists the murders at the family’s farmhouse in Essex were committed by Ms Caffell – a model nicknamed “Bambi” who was diagnosed with schizophrenia – before she turned the gun on herself.

It is a version of events that police initially believed, and Theroux says there are “legit” people who think Bamber is serving a whole-life prison term for a crime he didn’t carry out.

“Across the board you’ll find people who believe there were serious problems with the case, in terms of how it was investigated and how it was prosecuted,” he tells Sky News.

“There are things that are quite hard to explain on both sides.

“There was no forensic evidence of his presence at the farm, which is kind of extraordinary.”

Theroux says former detective Mark Williams-Thomas – who helped expose Savile’s sexual abuse – is one of those who believes Bamber “didn’t do it”.

He explains: “There’s a lot that’s positive about people attempting to find cases of historic crime in which there may have been an error.

“A lot of them are legit people. There are a lot of prominent journalists who would say they would feel Bamber is innocent.

“It’s not by any means a kind of fringe belief.”

While viewers are used to seeing Theroux feature in his documentaries, he is executive producer of The Bambers: Murder At The Farm, a new four-part series which re-examines the case and explores evidence that has emerged since the original trial.

It features first-hand testimony and previously unseen archive footage, as well as recordings of Bamber talking to a journalist while in jail.

So does Theroux himself believe Bamber committed the murders?

He remains tight-lipped on that, apologising for being “coy”, but admits the documentary has made him ask questions about who was responsible.

Theroux says: “Whether you think Jeremy Bamber did it or whether you think Sheila did it, both scenarios have anomalies, or at least require one to accept… surprising and in some cases seemingly anomalous details.

“The journey I went on was hearing something and going ‘If Jeremy Bamber did it, how did they explain that?’ – or ‘If Sheila did it, how would they explain that?'”

He adds: “Because of the nature of the case, we’re not in the realm of absolute certainty.”

The documentary’s makers had hoped to interview Bamber, but director Lottie Gammon says the Ministry of Justice refused to allow it.

She says some of those campaigning for Bamber’s release have “legitimate” concerns, including how police treated the murder scene.

“There’s a lot of question marks over their behaviour,” she says.

“No one really clearly explains – because they didn’t really have to during the trial – how did he do this crime? That’s not something that was nailed down.

“Because there are these loose threads, many loose threads, it’s easy for people to look at it and have questions.

“I think this case is quite suited to the online world now of deep diving into these cases – especially over lockdown, these groups have really proliferated.”

Bamber has lost several legal challenges over his conviction since the original trial, including an appeal which was dismissed in 2002.

At the time, the Court of Appeal judges said the more they examined the detail of the case, the more likely they thought that “the jury were right”.

They also concluded there was no conduct by the police or prosecution which would have “adversely affected the jury’s verdict”.

In 2011, Bamber contacted Ofcom over a documentary about him which he claimed invaded his privacy – but the complaint was rejected.

Theroux believes the convicted killer will “probably take issue with parts” of his latest series.

“Whether or not you believe he did it, he’s on a campaign to have himself freed,” he says.

“I think he’d appreciate the fact we’ve done a nuanced and forensic view, but we’ve clearly included material that undermines or disputes that (campaign).”

The four-part series, airing on Sky Crime, has been made by Theroux’s production company Mindhouse, which he founded with his wife, producer Nancy Strang, and fellow documentary maker Aaron Fellows.

Now aged 51, Theroux says he intends to keep making documentaries for another “good 25 to 30 years”.

“You could either say that’s a lot or a little,” he adds.

“The stories I most enjoy are not overly cuddly. I think there’s a reason I’ve been on BBC2 for 25 years, as opposed to BBC1.

“I’m interested in stories that have a dimension to them that is in some ways troubling.

“I don’t think you should shy away from the troubling side of life – that’s sort of my bread and butter.”

But despite the recent success of his celebrity interview podcast Grounded, a reboot of Theroux’s TV show When Louis Met… – when he famously spent time with the likes of Savile, Max Clifford and Neil and Christine Hamilton – isn’t on the cards.

“I’ve got a lot older. Times have changed, TV’s changed,” he says.

“It would be like doing Weird Weekends again. It would be quite weird, wouldn’t it?

“I would never rule out doing programmes that feature celebrities in… a single person profile, or go on a journey with someone and I’m on camera. I could see that happening and that would be fun.”

The Bambers: Murder At The Farm will premiere on Sky Crime and NOW on Sunday 26 September at 9pm.