Peacock’s new scripted series Devil in Disguise: John Wayne Gacy is now streaming, and dramatizes the arrest, investigation, and incarceration of one of America’s most notorious serial killers, John Wayne Gacy (Michael Chernus).

Arrested on December 21, 1978 in Norwood Park Township, Illinois, Gacy was the primary suspect in the disappearance of local Des Plaines teenager Robert Piest. He was taken into custody after police entered his house with a second search warrant, where they discovered multiple bodies in Gacy’s crawl space. The next day, Gacy confessed to murdering approximately 30 young males, including Piest. The case and its coverage shocked Illinois and the nation, and continues to have repercussions on how we respond to missing children and investigate sex offenders to this day.

The series was created by Patrick Macmanus (Dr. Death), and based on Peacock’s 2021 docuseries John Wayne Gacy: Devil in Disguise, which used new interviews and NBC News archival footage to tell Gacy’s story. For Devil in Disguise, he cast an impressive ensemble of actors who embodied the authenticity of the region and era. NBC Insider spoke with Chernus (Severance), Marin Ireland (Materialists) and Gabriel Luna (The Last of Us) about how they transformed themselves into their real life counterparts.

Michael Chernus watched real footage to prepare for Devil in Disguise: John Wayne Gacy

In bringing John Wayne Gacy to life, Chernus told NBC Insider that he first looked to John Wayne Gacy: Devil in Disguise to get a sense of the man behind the infamous crimes.

“We have the benefit that our show is based on the brilliant documentary that Peacock made about this case, so we all started there,” he confirmed. “I also did a ton of my own research, just watching every documentary and random YouTube video I could find, every podcast and every book. In consuming everything I could consume about this case, I found that some of it was really insightful and some of it was really not because this case was covered ad nausea from 1978 until today.”

Chernus said the docuseries and its outtakes provided by NBC News was his primary resource to study Gacy’s accent, body language, and intense countenance.

A native of Rocky River, Ohio, Chernus said that his Midwest origins gave him lots of exposure to the familiar “Rust Belt” accent that he heard in Gacy’s voice. “There was a familiarity to some of the sounds and melodies and rhythms of the way he spoke that already exists within me, in my memory and in my history. It’s a Chicago/Midwest dialect, but it’s also coupled with his weird, unique way of speaking.”

The actor also discovered that Gacy had a slight lisp and grew up in a Polish neighborhood. “He grew up hearing people speak Polish, so that affected the melodies and rhythms of the words he spoke. And he was always kind of putting on an act. He was trying to manipulate people and fit in, so sometimes the dialect is a little thicker when he’s trying to be ‘one of the guys,’ you know. And then in other moments, it’s not there nearly as much because he’s dropping the mask a little bit.”

Marin Ireland talks portraying Elizabeth Piest’s grief in Devil in Disguise: John Wayne Gacy

Marin Ireland portrays Elizabeth Piest, the mother of Gacy’s last victim, Robert. In the series, Piest evolves from an average, suburban wife and mother, to a tireless advocate for the memory and rights of her murdered son.

The actress explained to NBC Insider that she started with archival footage of Piest, but “I found when I started looking that there wasn’t a huge backlog about her. I took that as an indicator that I could give her some real privacy in terms of who she really was.

“So, what I really focused on was reading a lot of first person memoirs and books from people who had had lost children, or had experienced a very sudden loss,” Ireland continued. “Reading about their experience of their own grief over time … allowed that to just sort of live in my body and understand how I could sort of bring that to each scene along the way.”

She said that it was also particularly helpful to read the last episode of Peacock’s new series, “Jeffrey,” because it gave her a clearer idea of Piest’s whole journey.

“In one of the last scenes, she has with her husband when all the families are waiting together in a holding space at the end of the series. That was in one of the first scenes that I read for Patrick, and that scene stayed with me throughout,” Ireland detailed. “Knowing where she was going in that relationship, we could then track backwards as we went because I knew that scene was coming. It also felt like that scene was one of the most grounded places we’ve seen of her, and one of the most full of grace, in many ways. I think the grace that she has in that moment feels very, very profound to me and feels like her.”

Gabriel Luna takes on emotional weight of playing Rafael Tovar in Devil in Disguise: John Wayne Gacy

One of the first investigators to discover the truth inside Gacy’s home, Detective Rafael Tovar started a new chapter of his career with the Gacy case, having recently shifted from narcotics to violent crimes and cold cases. After getting a tip about missing Robert Piest, the Gacy case would consume the majority of his police career.

To play Tovar’s unease and despair with the case, Luna told NBC Insider that he sought interviews with the real detective to gain insight and perspective.

“First and foremost, I wanted to show him as what he represented, which was this individual a bit on the margins himself,” the actor explained. “He’s a bit of an outsider within his own police community. I wanted to show his ambition, what he really cared about, and how he was fighting to prove himself.”

Luna pointed to Tovar’s first scene, when he’s assigned by Lt. Joe Kozenczak (James Badge Dale) to follow up on a missing teen. “The first time you meet him, he himself is kind of dismissive of this case, like, ‘Oh, it’s a missing kid? Give me something else. Let me prove myself.’ Little did he know that this would be the defining case for his entire life.”

Luna said the series portrays Tovar’s transition into a “crusader” for these victims. “That is a role that he carried with him, and he still does to this day,” he said. “In every interview you see him in his latter age, he touches on how it’s really been his life’s work. I wanted to go on that journey with him in that transition towards fighting for the reclamation, the restoration of the humanity of these kids, in trying to root out where the neglect happened, where the wrong turns were made, doing his best, in our story, to help reform all of that.”