The multi-part documentary series explores the crimes of Joseph Naso, a convicted serial killer awaiting execution at San Quentin for the murders of four women. With the help of an inmate who shared death row with Naso, Mains identifies new victims and brings closure to their families, while offering audiences a rare glimpse into the mind of a detective who specializes in the unsolved.

“I’ve been a cold case detective for over 10 years, but I’ve never seen anything like this,” said Detective Mains, who recently spoke with The Express about the groundbreaking revelations in his new series.

“A detective sometimes will go his whole career without solving one cold case. Here, I was fortunate enough to solve four just for this show,” he said.

It began in 2022 with a letter sent from San Quentin’s death row in California. Sent by inmate William A. Noguera, who was sentenced to death for the “cruel and vicious” murder of his girlfriend’s mother, the letter contained information that set Mains on the path to unraveling several cases deemed unsolvable.

“It is because I am on death row that I was able to gather information and evidence that can possibly solve the riddle of several unsolved murders,” Noguera wrote to Detective Mains.

Seeking someone with the experience to follow his lead, he contacted Mains, whose work has been featured in the History Channel docu-series “Hunt for the Zodiac Killer” and Discovery’s “Conspiracies Decoded,” and who hosts a popular YouTube series he records from his home, “Unsolved No More.”

In 2024, Mains made local headlines for advancing the investigation of Centre County resident Brenda Condon’s 1991 cold case, which featured on his YouTube series.

“When he reached out to me through his attorney, I was a little trepidatious,” Mains said. “Why is a convict reaching out to me from San Quentin death row?”

“In short,” Noguera said, “I need you to put the puzzle together, which I cannot do from prison.”

In 2023, Noguera was assigned to San Quentin’s Yard 7, which houses some of California’s most notorious killers: Richard Ramirez, the Night Stalker; William Suff, the Riverside Prostitute Killer; and Rodney Alcala, the Dating Game Killer.

“But this particular serial killer is the worst monster I’ve ever run across,” Noguera told Mains over the phone. “He is by far the most refined at hiding himself, and that’s what made him such a premier predator… his name is Joseph Naso, and he has a lot of secrets.”

Over 10 years, Naso confessed the grisly details of his crimes to Noguera, who secretly turned the revelations into more than 300 pages of meticulous notes, striving to, in some small way, redeem himself for his own offenses.

To confirm the validity of Noguera’s notes, Mains requested evidence he could examine more closely. A former undercover narcotics agent with the Williamsport Bureau of Police, he said he knew how to handle a potentially reliable informant.

“He sent me some information, and I checked it out, and we were off and running,” Mains said.

Using details Naso had boasted about regarding a girl from Berkeley he murdered, Mains connected the story to the 1976 missing persons case of Lynn Ruth Connes.

“All the details matched — details that Bill Noguera wouldn’t have known,” he said. “Right then and there he had my attention, and I knew he was credible.”

From there, he plunged into the investigation.

“A real cold case detective doesn’t just sit on his ass behind a keyboard and spout off nonsense. They got to get off of their butt and go knock on doors, follow leads up. If that means tramping through a forest looking for bones, that’s what you do,” said Mains, who traveled the country and spent hundreds of hours working the investigation.

Throughout the show, viewers will watch Mains use his skills as an ex-FBI investigator to uncover three additional previously unidentified victims and expose one of America’s most prolific serial killers in real-time.

During Naso’s 2013 trial, in which he defended himself, the former photographer — known for photographing his victims — was convicted of murdering four women from a list of 10 that investigators believed represented his personal greatest hits. Mains believes Naso killed 26 times, leaving roughly two-thirds of his victims unidentified.

Though he cannot be certain, Mains said the details left him little doubt. Naso told Noguera he had killed 26 people, and everything else he shared had proven accurate.

“I know the type of person Joe Naso is,” Mains said. “He wants reminders of his murders. That’s why he keeps trophies.”

After learning that, Mains reviewed the search warrant from Naso’s house and made the chilling confirmation.

“I bet you, if 26 is the real number, he’ll have something relating to 26,” he said. “Lo and behold — on, like, page seven of the search warrant, I saw that police had taken a coin collection of 26 coins.”

Throughout his career, Mains has maintained that he does this work on behalf of victims’ families. For the show, he met with three, which he says deeply impacted him.

“I shed a tear at every dining room table I sat with them at,” said Mains. “You will see every emotion you can imagine course through their veins because it’s bringing up all these emotions that have been dormant for so long… they run through it all — the disbelief, the anger, the sadness, the hope, the love, the gratitude, the respect, and I think that’s what’s special about this show — you get to see that.”

Above all, he says they want to be heard, “If they can run that through me, and I can be that voice, I’ll take on that responsibility.”

Mains said he hopes his new show achieves that in a factual way that respects the victims and avoids exaggeration.

Mains, who was recently named Head of True Crime Development for Fireside Pictures and consulting producer of the show, said that as one of the new faces of true crime in Hollywood, he’s working to bring honesty and integrity back to the genre.

“They do things for clicks, and what happens is sometimes you start saying things that aren’t true, and I don’t like that, especially in true crime, because it affects victims’ families,” he said. “I don’t like sensationalism in true crime. I want facts, honesty, truth, transparency — to me that’s paramount in life, let alone true crime.”

Though he is enjoying this new role, Mains says investigation will always have his heart, “I will always be a detective… Anything else I do in life will come secondary to that.”

Despite the countless hours poured into the investigation, some answers remain out of reach. Mains never spoke to Naso directly.

“He was going to call me, I had my phone ready, but he never called… If you want to be at the top of your game, you’ve got to learn and ask the question, why? And you have to talk to the people that have those answers, and Joe Naso has those answers, and I want to know.”

Mains doubts he’ll ever hear from Naso but admits he can’t be certain.

“I don’t (think he will call), but the reason I am a little hesitant is because if he watches this show, then he may,” said Mains. “He’s very narcissistic, and he may want to get a point across to this cold case detective… he has my number to do that.”

A particularly chilling detail for local readers is that Naso was once a Little League coach — a reminder, Mains says, that predators can hide in plain sight.

“I’ve done hundreds of search warrants in people’s houses, and I’ve seen things in those houses that, when I saw the person in the grocery store, I would never have thought would be in their home,” said Mains. “Because of that, I am very aware of my surroundings and I know that there’s monsters among us, and that’s why you have to be very vigilant and be aware of your surroundings at all times.”

The series debuts on Saturday, Sept. 13 at 9 p.m. ET/PT on Oxygen with a special two-hour premiere. It continues with two back-to-back episodes on Saturday, Sept. 20, in the same time slot.

“Death Row Confidential: Secrets of a Serial Killer” is produced by Wolf Entertainment, Fireside Pictures, Universal Television Alternative Studio, a division of Universal Studio Group, and Vanity Fair Studios. Dick Wolf, Tom Thayer, Jason Wolf, Patrick DeLuca, Helen Estabrook, Sarah Amos, Claire Howorth and Liz Yale Marsh serve as executive producers. Kevin Brennecke serves as showrunner.