William Friedkin, director of "The Exorcist," was attracted to his latest shocker, "Killer Joe," because playwright Tracy Letts' script reminded him of his adolescence in Chicago.

"I grew up with people like that," said the Chicago native when he visited the Seattle International Film Festival in June. "I understood them. And I don't pass judgment on them. I found them fascinating."

The cast of characters includes a deeply desperate drug dealer, Chris Smith (Emile Hirsch), who comes up $6,000 short and hires a Texas hit man, "Killer Joe" Cooper (Matthew McConaughey), to murder his own wretched mother. Her insurance money will presumably pay off the debt and make the family rich.

Also part of the scheme are Chris' blithely amoral father, Ansel (Thomas Haden Church); the boy's slightly more sympathetic stepmother, Sharla (Gina Gershon); and Chris' trashy sister Dottie (Juno Temple), whose sexual favors are promised to Cooper as part of the deal. The trailer-park setting couldn't be more appropriate — or stereotypical.

"Killer Joe," which is based on Letts' 1993 play of the same name (he later won a Tony for writing "August: Osage County"), shifts wildly between a brutal crime drama (it's one of the few movies to earn an NC-17 rating primarily for its violence) and a darkly comic contemporary fairy tale.

The violence takes over in the final scenes, which are shockingly crude even for a Southwestern gothic melodrama. Yet the movie frequently clicks as a sendup of over-the-top film-noir storytelling.

Church's laid-back performance nails it. So does McConaughey's drawling seducer, who is just as funny as the confident rogues he played earlier this summer in "Bernie" and "Magic Mike." (His hired killer is also a cop.)

Unfortunately, their scene-swiping triumphs often leave the other actors high and dry. Hirsch and Gershon seem to be performing in a different, dumber movie.

John Hartl: johnhartl@yahoo.com