David Fincher has made a career of delving into abnormal minds, with Seven, Fight Club, Zodiac, The Girl With the Dragon Tattoo and Gone Girl. But he says his newest project, Mindhunter, isn’t about psychopaths. It’s about the people who figured out how to hunt psychopaths — and that’s an important distinction.

Fincher produced and directed four episodes of the addictive new Netflix show, which starts streaming Oct. 13. The series is about the agents who interviewed the likes of Charles Manson and the Son of Sam in order to better understand the psychology of mass murderers. By doing so, they created a psychological profile for these killers that would allow the FBI to catch similar psychopaths more quickly in the future.

The show is based on the real life events chronicled in the book Mindhunter by the FBI agents who coined the term “serial killer.” But Fincher says he struggled with how deeply the show should dive into the details of these grisly murders. “I said many times as we were in the process of making the show, ‘Wait a minute, we’re making this show about serial killers. We’re not making this show for serial killers,'” the director says.

Fincher spoke to TIME about why he hates the idea of becoming the “serial killer director,” casting the cheery Glee star Jonathan Groff in a dreary role and why we’re all so obsessed with true crime stories.

TIME: Why did you decide to produce and direct several episodes of Mindhunter?

David Fincher: I was fascinated by the notion that at some point, [J. Edgar] Hoover’s creation — this monolithic, bureaucratic organization — had to say, “There are things going on that we just can’t properly articulate and don’t understand. How do we protect the innocent from it until we look at how it all works?” And even if it started in the basement, even if it started in a way as the kind of voodoo department, they did it.

I also thought it was an intriguing that in order to truly understand one’s enemy, one had to develop even for short periods of time — even if they were faking it — empathy for people who heretofore would have been beneath our contempt. They had to figure out how to have human conversations with those who are subhuman.

The show sets up this shift from explainable crimes motivated by jealousy, greed, etc. to seemingly senseless violence. Do you think that shift actually took place or the FBI just started paying more attention to the senseless crimes?

I think serial murder or psychosexual sadism has existed for forever. In Eastern Europe, the mythology of the vampire or the werewolf is probably a by-product of this kind of behavior. A mutilated body found in the forest had to be attributed to something. We’ve allowed it to become the mythology of horror, but that activity probably had more to do with psychosexual sadism than it does with lycanthropy.

I don’t know that there was more of it. But there was really a public disturbance where people suddenly began to understand their own vulnerability to aberrant behavior. I remember Zodiac. I definitely remember thinking, “What’s going on? Why is this person who’s writing letters to the Chronicle so angry at kids at Lover’s Lane? What did they ever do to deserve this?”

How closely does the show adhere to the true story?

Joe Penhall was the first person to say, “I think I can do a better job of dramatizing this if I’m given the leeway to take some of the attributes of this person and some of the attributes of this person and create a new character.” So that’s what we did.

A lot of [the interviews with serial killers] were taken verbatim. The Kemper interviews, the Manson interviews — that stuff is pretty well documented. We stayed as close to that as we could while still having a dramatic arc. I don’t think we attribute anything to Kemper that he didn’t say. I mean, he may not have used the word oeuvre.

How did you cast Jonathan Groff? He’s known for much jollier roles.

He had auditioned for The Social Network, and I was really taken with him then too. The world he occupies in this show is a lot more dour than Glee. But I hope I can direct more than just interviews with psychopaths. And I know that he can do more than musical theater.

What do you want Jonathan to portray emotionally in the scenes where he’s interviewing serial killers?

He’s obviously the avatar we experience the story through. I think one of the odd things about this show is how Holden-centric it is. It’s very much like Chinatown where there’s not a moment where you’re not with Holden. I think there were 8 scenes out of 175 that he didn’t shoot. And that’s a very rare thing for television.

I don’t know that you direct Jonathan. You explain the circumstances, and you unleash him. He just wants to tear it up. My biggest thing with Jonathan was always, “Stop smiling!”

What do you make of the true crime boom, from podcasts to TV?

I think there are a lot of people who see themselves as detectives. Certainly, when you see things like The Keepers or listen to Serial, you can see that some people just get their righteous indignation stoked. Some people are always fascinated by puzzles and the political obfuscation of solutions, because ultimately investigations do bear the weight of political ramifications.

Why do people seem more intrigued by these subjects now?

In the information age, there’s more to excavate. There’s more access to what Marcia Clark is really thinking or what the Menendez brothers did the day after. We’re very quick to judge. That should be looked at as a human failing. But I think at its best, people’s interest in true crime is people’s interest in trying to understand why we behave the way that we do.

Is that the purpose of this show?

I think so. I said many times as we were in the process of making this, “Wait a minute, we’re making this show about serial killers. We’re not making this show for serial killers.” Everyone wants to be as detail-oriented as possible, but at a certain point you have to ask yourself, “There is a prurient nature to this. Are we feeding that? Do we want to know more about humanity or do we want to know about inhumanity?” That’s always a hard question. Unfortunately, ultimately, it comes down to taste.

Is that something you struggled with with Seven or Zodiac?

I used to say jokingly that by the time we got to the sixth weekend of Seven, anybody who is there for the matinee should probably be submitted to a thorough background check.

At the same time I was also very sensitive to people who would say, “Oh, you did Seven. You’re the father of torture porn.” And I would say, “No. They talk about torture in the movie, but you don’t live through it. It’s not about enduring it for dramatic purposes.”

So it’s that thing: Are you going to be part of the solution or are you going to be part of the problem?

You’ve previously chafed at this notion that you are the “serial killer director.” Did you worry at all that doing this show would bolster that image?

I took on this project in spite of that, because this show is not about serial killers. This show is about FBI agents, and how they were able — through the application of empathy — to understand those people who were so difficult to understand. That was what was intriguing to me. I don’t need another serial killer title on my resume. This was not about that. It’s like in Zodiac — you never know who this person is. And in this show, he’s right there and he might talk to you.

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Write to Eliana Dockterman at eliana.dockterman@time.com.