Martin Freeman is no stranger to playing a detective: One of his best-known TV roles, after all, is as Watson in “Sherlock.” Now, Freeman stars in the true crime series “A Confession,” premiering May 12 on Britbox.

However, “A Confession” diverges from Freeman’s norm as it portrays a real-life story; specifically that of Steve Fulcher, a detective who in trying to catch a woman’s killer, triggered the downfall of his own career. Freeman and director Paul Andrew Williams joined Variety senior editor Michael Schneider in the Variety Streaming Room presented by Britbox to discuss the real Fulcher’s visit to set, handling tough scenes and what makes “A Confession” different from other British crime dramas.

Freeman was initially attracted to the project because of Williams – the two worked together previously on 2015 film “The Eichmann Show” – as well as the heartbreaking good intentions behind Fulcher’s motivation to solve the case.

Fulcher led the real-life police investigation into the disappearance of 22-year-old Sian O’Callaghan in 2011, which led to the arrest of taxi driver Christopher Halliwell — who ultimately was also accused of the murder of another woman, Becky Godden-Edwards. Fulcher, however, was penalized for his method of interrogating Halliwell before bringing him to the police station — although at the time he did so in the hope of finding O’Callaghan.

“I was shocked by what was happening, by what befell this man for simply trying to do what any of us would want a copper to do. He wasn’t going seriously Maverick. He wasn’t going Liam Neeson in ‘Taken,’ do you know what I mean?” Freeman said. “What he did was completely kosher.”

So when Fulcher and his family actually came to visit the set of “A Confession,” the impact and responsibility of the show became even more apparent to both Freeman and Williams.

“It’s the first time I’ve played someone who’s actually come to set and watched,” Freeman said.” I think once I’d met him, I gathered that he was happy that I was doing it; as in, the whole thing had his blessing.”

Added Williams: “I think when [Fulcher] watched it, it just reiterated how unfair it was and how crazy that situation was. When you are doing the right thing and it’s just injustice – which everyone can see is ridiculous – that’s very hard to get over.”

A show with emotional subject matter brings tough scenes, but Freeman credited the rest of the cast – including Siobhan Finneran, Joe Absolom, Charlie Cooper, Imelda Staunton and Daniel Betts – with allowing him to get away with “not acting.”

“When you’re working opposite very good actors, a lovely thing is you don’t have to do any acting. You don’t have to really bring anything except your presence and to be open to the moment,” Freeman said. “I got very emotional, but I didn’t even want to. That wasn’t me trying to do a number as an actor, it’s like you’re just reacting to what you’re being given.”

According to Williams, the real, raw quality of both the emotion and the material is what separates “A Confession” from other British crime dramas.

“The British crime dramas, a lot of them don’t really push the reality of crime, of murder, of horrible, horrible things because it is a form of entertainment,” Williams said. “You know, you look at ‘Murder She Wrote,’ it was brilliant, but I didn’t believe it happened, whereas things like ‘A Confession’ and other shows where you’re like, ‘I believe this and I genuinely am emotionally invested in to it.'”