Perhaps it won’t surprise you to learn that Holt McCallany, the brawny, silver-haired actor who plays special agent Bill Tench in David Fincher’s Mindhunter, is mildly obsessed with serial killers. To prepare for the true-crime Netflix series’s second season, McCallany tried not once, but twice to visit David Berkowitz, aka the Son of Sam, at the Shawangunk Correctional Facility in New York.

The first time he went, he missed the window for visiting hours. The second time, Berkowitz refused him. “He’s been very vocal about not wanting to rehash the details of the murders,” McCallany said in a recent phone interview.

In the late 1970s, Berkowitz terrorized New York, killing six people and injuring seven; at one point he claimed that a dog told him to do it. Now 66, Berkowitz has reportedly converted to Christianity. “He calls himself the Son of Hope. He’s no longer the the Son of Sam. He does get visitors frequently, but they’re people from the church,” McCallany said.

The actor also reached out to the real Ed Kemper, a six-foot-nine killer who murdered 10 people—including his mother and grandparents. (He’s played in the show by Cameron Britton.) But Kemper never responded. So McCallany went to the California Medical Facility, where Kemper is housed. “When I got there, what I discovered is that Kemper has kind of given up on life,” the actor said. “He’s confined to a wheelchair. Do you know what I mean? He doesn’t really take visitors. He doesn’t bathe himself anymore. It’s very sad.”

But while he didn’t meet with Kemper, McCallany was ultimately able to meet Bobby Beausoleil, the former Manson Family member who murdered musician Gary Hinman in 1969.

“I have to tell you, we had a very interesting conversation. I spent about four hours with him,” McCallany said. He even found himself feeling sympathetic toward the ex-cult member, who had previously been denied parole 18 times. Beausoleil was on track to have his parole granted, but California Governor Gavin Newsom reversed the parole board’s recommendation earlier this year.

“I’ll be honest with you: I disagreed with that decision,” McCallany said. “I mean, look, he killed that musician Gary Hinman. But it was 50 years ago. He was 21. He was high on drugs. He’s showing remorse...having met him and having spoken to him, I bet anything that he will never commit another crime.”

“If he wasn’t tainted by his association with Manson, he would’ve been paroled many years ago,” McCallany added.

Now, before you get the wrong impression: McCallany isn’t just a twisted, macabre true-crime tourist. He pursues meetings with all of these notorious figures for work, he said, conducting research that feeds back into his portrayal of Tench. On the show, Tench is the good cop to Holden Ford’s (Jonathan Groff) bad cop, a moralistic husband and father who grimaces his way through interviews with vicious killers. The studious actor side of McCallany wanted to know what it’s really like to sit across from those guys and talk to them; the sympathetic, human side of him wanted to know if guys like Berkowitz had really changed during their time behind bars.

“His conversion to Christianity and things that he’s done to try to change his life, are they sincere?” he mused. “Because when you talk to guys in law enforcement, and some of them are good friends of mine...I’m not sure they really believe in rehabilitation.”