Laura Greenberg was a journalist determined to understand why people kill. In her search for answers, she befriended a long-forgotten serial killer behind bars. As he described his crimes, her sense of reality began to unravel.

Greenberg’s unsettling bond with Doug Gretzler — who, along with accomplice Willie Steelman, killed 17 people, including two children — continues to haunt her decades later. Her search for understanding is the focus of Oxygen’s new true-crime documentary, “Charmed by the Devil.”

The film explores how Greenberg visited Gretzler 350 times, exchanged hundreds of letters and recorded more than 500 hours of audio in a relentless effort to, as she put it, “understand the monster.”

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Growing up, filmmaker and Nickelodeon voice actor Ben Giroux only knew that his aunt was interviewing “a guy who killed somebody.” It wasn’t until 2020, during the pandemic, that he gained full access to Greenberg’s startling recordings.

“She always says there are 17 bodies between them,” Giroux told Fox News Digital. “He was a monster. He was the devil. And yet she was able to look beyond that and establish a human connection. She says she wouldn’t put a label on what that connection was. I’m sure her answer changes daily on how she would define it.”

Giroux noted that the depth of that connection is what makes the story so unnerving.

“When you walk into her house, it’s basically a museum dedicated to this case,” he shared. “There are police reports, crime scene photos, written letters and paintings. It’s a massive trove of communication between her and Gretzler. It’s an obsession. I think they came to both rely on and become codependent on each other in that obsession.”

Gretzler and Steelman landed on death row after a three-week killing spree in Arizona and California. Steelman died of cirrhosis of the liver in 1986 — the same year that Greenberg, a scrappy reporter for City magazine in Tucson, got a tip about Gretzler that sparked her curiosity.

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Greenberg first contacted Gretzler by letter, hoping to gain his trust. At the time, he refused to discuss his crimes with anyone. Still, her words intrigued him enough to respond. What followed was an unbroken exchange of letters and recorded conversations. Soon after, she visited him in prison.

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“Gretzler was somebody nobody had ever heard of because the only person he was talking to was my aunt,” said Giroux.

The boundaries blurred quickly. They bonded over their shared New York City upbringings. Greenberg, who was living with a boyfriend at the time, would wait until he fell asleep, then quietly lock herself in the bathroom, draw a bath and, as she later described, listen as Gretzler spoke in detail about the murders. At one point, he professed his love for her and grew increasingly jealous after she married.

“No one knew these tapes existed until now,” executive producer Lauren Flowers told Fox News Digital.

“I was surprised by how ordinary some of these conversations were, knowing the intention was to hear about gruesome crimes and uncover the why. Then you put on another tape and hear them talk about the weather or music, what Laura was buying at the grocery store — even realizing they once went to the same music festival and hung out at some of the same places.”

Flowers noted that the documentary raises difficult ethical questions about how close a journalist should get to a story. The unusual access Greenberg gained — and the intimacy that followed — will likely raise eyebrows among viewers, she pointed out. Giroux and Flowers said the film explores Greenberg’s pursuit as professional boundaries are tested.

Gretzler gave Greenberg detailed accounts of his life and crimes. At 22, he fled his responsibilities as a husband and father in New York and headed to Colorado, where he fueled his days with drugs and alcohol. 

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There, he met Steelman, a volatile 28-year-old who had recently been institutionalized. They formed a “pact,” with Gretzler pledging absolute loyalty to Steelman, whom he considered a brother.

Together, they embarked on a cross-country trip with a simple plan — to steal money and drugs. It quickly spiraled into something darker. Gretzler said flatly that it didn’t take much for him to kill.

While some families said the interviews helped answer lingering questions, Greenberg acknowledged that no explanation could ever justify the brutality of the murders.

As Greenberg gathered information, she reached out to loved ones of the victims and to Gretzler’s sister. They opened up to her for the first time.

“On the surface, it’s confusing,” Giroux said. “Wouldn’t they reject someone who became so close to a person who took so many lives and devastated so many families? But I think they’ve come to appreciate her ability to find the truth and dig for every detail. It speaks to her obsessive personality.”

“She got everyone talking — everyone connected with her,” Giroux said. “She has a real gift for getting people to open up. She certainly did that with Gretzler, who rarely spoke to anyone else. She wanted to leave no stone unturned.”

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“Does she accept that boundaries were crossed? I think so,” Giroux said. “She’s incredibly transparent and candid about it. She doesn’t shy away from discussing things that would make others flinch. She’s remarkably open about how deep that connection became.”

Greenberg said she felt “disgusted” as Gretzler revealed the darkest details of his murders. He spoke not only about the killings, but also about a chaotic childhood, including the death of his teenage brother. She repeatedly challenged him, making it clear that no explanation could excuse the scale of his crimes.

Greenberg pushed Gretzler as she studied how violence took root in his life and how he justified his heinous acts. For some of the victims’ families, the interviews clarified how and why the crimes unfolded, filling in gaps that police files and court records never fully answered after years of unresolved questions. It gave them a painful understanding of what happened to their loved ones during their final moments.

“We wouldn’t have reached anyone without Laura,” Flowers said. “Everyone we found said, ‘Do you know Laura Greenberg? You have to talk to her.’”

“That was especially true with Dee Gretzler, Doug Gretzler’s sister,” Flowers shared. “She was just a kid when she learned about it at school. She lives privately, and this is the first time she’s ever acknowledged that her brother was a serial killer. But she knew that if Laura participated, she could tell her story.”

Gretzler invited Greenberg to witness his execution on June 3, 1998. She sat near his sister. In the years leading up to his death, they continued to talk about “everything in life, both profound and mundane,” said Giroux.

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“The finality hit her hard,” Giroux admitted. “What’s so strange is how normal their interactions sounded at the end — almost casual. You’d think the execution would be the end of the story, but I think it was the beginning. Her obsession only grew after that, and her commitment to telling every detail of this story intensified after he was executed.”

What remains unchanged are the lives lost.

“I think Laura got Gretzler to accept that the responsibility was his,” Flowers said. “There are a lot of people with s—– childhoods who don’t kill 17 people — something she reminded him of repeatedly. From the start, we felt a responsibility to the victims and hoped to provide some closure to their families.”

“The thing to take away from my aunt’s connection to Gretzler is the danger of obsession — and how we all need to check ourselves,” Giroux said. “You don’t want to go too far down the rabbit hole. This has consumed 40 years of her life.”

“Charmed by the Devil” is available for streaming on Peacock.