Liev Schreiber went the extra mile when prepping to play Jonah Lynn, an ex-soldier turned homicide detective in Apple TV‘s psychological crime thriller, Nocturne.

The series, based on The Sandman and Lazarus novels by Lars Kepler (husband and wife co-authors Alexander Ahndoril and Alexandra Coelho Ahndoril), sees Jonah unearth an investigation into Jurek Walter (Stephen Graham), a man suspected of taking more than a half dozen lives and kidnapping two young siblings. Though the homicide detective retired shortly after Jurek got locked up, when one of the siblings presumably taken by Jurek resurfaces three years later, Jonah — tormented by grief, regret, and his complex history with the master manipulator — returns to the case that broke him and his family.

In an interview with Decider, Schreiber shared what steps he took to get into Jonah’s dark headspace and delivered an authentic, quietly devastating performance.

“I met with a really interesting group of Pittsburgh homicide detectives. We went to a bar, had a few drinks, and had some very candid conversations,” the Nocturne star revealed over Zoom. “One of the things that struck me was the idea that these guys are witnesses to the worst of humanity all of the time. And that’s a lot to carry — that your job is to be a witness to the worst elements of human behavior every day. What do you do with that?”

Though Schreiber knew he couldn’t fully comprehend the trauma and emotional toll of the job, the deep conversations and shared experiences gave him crucial insight and perspective heading into Nocturne.

“It creates a very specific relationship with each other, a feeling that only they know, which is something I’ve heard in interviewing vets with PTSD who’ve been to war — that only the people who’ve witnessed the horror that they’ve witnessed can understand how they feel,” Schreiber said. “There was something really compelling about trying to understand that, trying to relate to that, asking those guys what it was like the first time they saw a deceased person and what it’s like now. That became a very emotional conversation for all of these guys, as they talked about how inured they had become to death and what that does to a person.”

Schreiber, also an executive producer on Nocturne, credited the real-life Pittsburgh homicide detectives and veterans for giving him his “inroad to Jonah,” a former tracker for the U.S. Army Rangers, and helped him realize that the character had “a tough set of memories to carry around with [him].”

In Nocturne‘s production notes, director Allen Coulter further praised Schreiber’s performance, saying, “Liev wanted it to be real and not false or arbitrary. Everything had to make sense within our world. Off camera, he’s very funny but Jonah is such a straight and narrow, taciturn, man of few words. And Liev totally became that. Authenticity is paramount to him.”

In addition to Schreiber, Decider also spoke with Graham about the extensive work he did to transform into Jurek — from physical training and voice coaching to studying psychopathy, sociopathy, and even watching crime documentaries with his wife. Read more of our chat with Graham here, and be sure to watch Nocturne Episode 3 on Friday, November 6.

Stay tuned for more of DECIDER’s interview with Schreiber and the cast and showrunner of Nocturne.

New episodes of Nocturne premiere Fridays on Apple TV.