“Client 9: The Rise and Fall of Eliot Spitzer” is a documentary about the New York state attorney general who took on Wall Street, was elected governor, and then, in one of the most spectacularly scandalous falls of the last decade, resigned following charges that he was a customer known as “Client 9” of a high-end escort service that provided expensive prostitutes for wealthy men. Alex Gibney, who has made powerful documentaries about falls from grace: Enron, disgraced lobbyist Jack Abramoff, and post 9/11 torture by the US military, spoke to me about this film. (“Client 9” is now available at xfinity On Demand)

Why did Spitzer agree to do the film?

He wanted “final argument.” he wanted the ability to have his say in a film that was going to be all about him. He knew Peter Elkind from before and he knew we were going to do a rigorous and factual job. So, better to have his story told than not. We made a powerful argument that he was going to have to reckon with his past and that cooperating with us would be a way of dealing with it and then maybe he could move on.

You made an unusual decision for a documentary in having an actress play the role of one of the key players — and not be revealed as an actress until the end of the film. Can you talk a little about that?

She didn’t want her identity exposed, for obvious reasons. There’s a standard way to do that in documentaries — put the person in shadows and mechanically alter their voice. We experimented with that. It was terrible. It turned her into a cliche like a mobster, a monster, like she was in the witness protection program. It created an aura of criminality about everything she did, a cheap stereotype. So I thought, as long as we disclose it, let’s transcribe the audiotapes and then cut them down and that’ll be the script that an actress performs. It will be true to what she said, and more truthful by presenting her as a human being. I found her not just truthful but very affecting, not like the stereotype of prostitutes that we think of, smart and funny and tough. For all those reasons it seemed like the more truthful thing to do. At the end of the day, each film sets its own rules. Our obligation is to let the viewer know what those rules are and that can be accomplished any number of ways.

How do you decide what your rules will be in a given film?

I was very influenced by “The Thin Blue Line.” I heard a wonderful radio interview with Errol Morris where he said, “The only version of the truth I didn’t show was the version I thought happened.” I thought that was a very interesting rule and so I made it my mission from then on to come up with rules that I thought made sense from my standpoint and in terms of the overall presentation of the story. With “Angelina,” we show her two or maybe three times before we disclose that she’s an actress.”

I wanted her to be shocking and I wanted you to be saying, “Oh, my God, we’re really getting inside here” and to experience her as a person without thinking about the device. And then I reveal it but by then hopefully you’ve developed an affect with her as a person. And then you roll with it even though you know it’s an actress.

The movie digs in by having a whole bunch of false starts. It’s a movie all about about things that you think you know and you don’t know know. When you first see that guy in the cowboy hat at the beginning, you think “Why are they putting this painter up front?” And then you learn that he was the booker and he knew Ashley. And then you think that Ashley is at the center of the story and it turns out that she’s not. Nothing in this film is quite what it seems initially.

Why did Spitzer foe and business big shot Ken Langone agree to be in the film?

I think he wanted to be in the film because John Whitehead told him that I was a good listener and he enjoyed talking to us. I found it very refreshing talking to him. There were no handlers, just Ken Langone telling me what he thought. People talk when they’re emotionally invested in talking. As you can see in the film, he is invested in talking. All you have to do is say the name “Elliot Spitzer” and smoke comes out of his ears. He literally foams at the mouth. He is the essence of the “winner take all society.”

Do you think that Spitzer underestimated not just the power and fury of his opponents but his own ability to take on the very different job of being governor?

Spitzer was not comfortable with the culture of the legislature which was one of the great bogs of corruption, a system of greasing. He had a commitment to the power of argument to carry the day and was much more high-handed. I have sympathy for that idea in principle. But Spitzer had a great deal of difficulty in letting other people take credit for his ideas. That would have been smart. Weird rules, double-dealing, entrenched favors and interests. It’s so sclerotic; it’s terrifying.

What would you say that this film is about?

Unlike the film I did just before this, “Casino Jack and the United States of Money” where you could come out of that and say, “Take the money out of politics or we’re done,” this one is harder to summarize. It asks some fundamental questions about human nature and how we judge our public officials. Do we judge them as vehicles through whom we live vicariously or by what they do as public officials? Are we being blinded by scandal in a way that prevents us from seeing stuff that really affects us as individuals?