Matthew McConaughey continues a summer of jolting performances with Killer Joe, a movie about a family in Texas (comprised of Emile Hirsch, Gina Gershon, Thomas Haden Church, and Juno Temple) who have a wild scheme to kill Church's ex-wife for her insurance money. Hired to do the job is McConaughey's title character, who affects the twisted family in ways they could have never imagined. Playwright Tracy Letts wrote the screenplay for the film, based off his own play which was first staged in 1993. In 2006, Killer Joe director William Friedkin adapted Letts' play Bug for a film adaptation starring Ashley Judd and Michael Shannon.

I sat down with Tracy Letts to discuss his story, his relationship with now two-time collaborator Friedkin, and what his impression was of Matthew McConaughey's romantic comedies before Killer Joe came along.

Killer Joe opens in Chicago on August 3.

READ Jeff Bayer's "9/10" SXSW 2012 review of 'Killer Joe'

What literature were you reading when you wrote the play for 'Killer Joe' twenty years ago?

This story was written twenty years ago. I was reading some strong pulp fiction at the time, a lot of Jim Thompson, who is a great pulp fiction writer, originally from Oklahoma as am I. It's very black. It's very hardcore noir. I think one of the principal aspects of that kind of noir are people who want things really badly, who want and feel things really strongly, and yet who make some terrible decisions in their attempts to get them. I think something about that is very human, actually. There's something about that we can all identify with.

Where do you find the humanity with these characters?

We've all wanted something, and we've done absolutely the wrong thing to try to get it. These characters are working poor. I hear them described as working poor, and the truth is, they have jobs. They don't have any type of spiritual food, it seems, and what they believe is going to fix their problem, and fix their situation, is to acquire money. The fact that they live in a moral vacuum is frightening, but I always hoped, and we never wanted, to step back and point our finger and say, "Look at these people." We always wanted to say, "They are us. They are a manifestation of us on the fringe of our society."

When you go to write the screenplay for this 15-20 years after the play, how did you feel about going back to the characters? Was there any temptation to change them?

No, not really. I still have great sympathy for them, and I always did. I find them kind of touching, I don't know if other people do. It's always interesting to write something like this, and hope that it's going to have some lasting power. But what you don't anticipate is how it's going to travel through life with you. It's like this weird child that you have. It's so odd to have a relationship with something like this, but still watch this and go, "Man, that's some crazy sh*t. What was I thinking when I wrote that?" As bad as [these characters] get, even at their absolute worst, there is still part of me that sees something sad at the core of them. What does Joe represent to you?

Order in the chaos. There are rules that he clearly establishes. When he introduces order into their lives, there is a sense of, "Is this a good guy, is this a bad guy?" To have a moral code, as long as you have one, is that the starting point? I wanted to start the conversation, without having easy answers related to, "Who's the good guy, who's the bad guy, who is making the wrong decision?"

Matthew McConaughey has certainly won over a lot of hearts with this performance ...

Because we always knew he was good. We always knew he was actually good. Before this film, what was your impression of McConaughey - what had you seen of his work? How has that changed? When I first told friends Matthew McConaughey was going to play the role, they were like, "Aw shit, man." They thought it was bad news. I said, "I don't think it's bad news." Then they started to list his romantic comedies, to which I replied, "I haven't seen any of those, have you seen those? Those movies aren't made for me. I wouldn't go see those movies on a bet." There's nothing wrong with the guy making that money, and the movie people wanted to see. I am not the target audience for that stuff, and never was. But I remember Lone Star, A Time to Kill, and Dazed and Confused. All of his best performances, set in the south. And I saw Lincoln Lawyer recently. I think the guy is great. A lot of great actors have made really bad movies. He's really good in the film, and brings this timeless western quality. We were doing roundtable interviews ourselves, and this reporter said, "You're clearly not at all like this character, you clearly have nothing in common with Killer Joe," and I turned to him and said, "Is that true? You don't have even a little bit of the evil sonuvabitch inside you?" And he smiled at me. He's got a dark side to him that likes to express itself, and it's really interesting on film.

What's your relationship like with director William Friedkin? Will's a great guy. He's funny, and outrageous. He has been so gracious and generous to me, as a writer. He has great respect for writers. The first time had me out to his place in Los Angeles to make a movie about my play Bug, he told me what he was going to do, and then he did everything he told me. My experience in Hollywood was not that. When he first showed me Bug in an editing room, he said, "What'd you think?" I said, "I think it's great." To which he replied, "Do you see anything you'd change?" And then we ran the movie, and discussed what could be changed in the edit. He's a no bullshit guy. He moves that camera like Samuel Fuller; he knows what he's doing.

Here's a great story that Caleb Deschanel told me. [Friedkin] is notorious for only using the first, or perhaps the second take. It keeps everyone on their toes, including the crew. One day, they shot a truck pulling out. Caleb turned to him and said, "We have to reshoot that, you can see the camera crew in the reflection of the truck." Friedkin said, "No, we're fine, we're moving on." Caleb replied, "We've only done one shot!" And Billy said, "Caleb, don't you think audiences are sophisticated enough now to know that movies are shot with movie cameras? We're moving on." And he was right - by the time the film was all shot and edited, you couldn't see the crew in the reflection.

Finally, was the usage of Clarence Carter's unusual love tune "Strokin'" something that you added to this script?

Nope, [laughs]. That was all Billy.