When William Friedkin was a boy he stumbled upon Orson Welles's movie masterpiece, "Citizen Kane." That moment changed the filmmaker's life forever.

"It opened my eyes," says the director of "The Exorcist" and "The French Connection."

"I knew then and there that I wanted to make movies. But ‘Citizen Kane' showed me that good and evil existed in all of us. It was all over those characters. That was a revelation for me," Friedkin explained as we chatted in a trendy downtown loft during the Toronto International Film Festival.

Fast forward to 2011 and the 76-year-old legend is still pondering that thin line between good and evil. But evil has the upper hand in his lurid new crime thriller, "Killer Joe."

In this blood-splattered tale starring Matthew McConaughey, murder, betrayal and rough sex involving pieces of Kentucky Fried Chicken push the boundaries of good taste in unspeakable ways.

As this noir thriller opens, a cash-strapped drug dealer (Emile Hirsh) hires a dirty Texas cop to kill his loathsome mother, who lives in a trailer park but has a $50,000 life insurance policy.

But this isn't your usual contract murder. Killer Joe (McConaughey) insists on a retainer for his services: he wants his client's teenaged sister to be his sex slave.

The deal is done. The girl (Juno Temple) is whored out by her brother and father without so much as a tear or regret. But allegiances change, particularly when Joe and his sex slave fall in love.

"I like to think of this movie as a darker version of Cinderella," Friedkin said, with a grin.

"This girl's been used and abused by her family. Joe does the same thing. But he awakens her sexually. He becomes her prince charming in this strange, twisted way. When that happens everything changes. She can't go back to the way things were, not even for the brother she loves," he says.

Faithfully adapted from Tracy Letts' 1993 debut play, "Killer Joe" is soaked with low-life smells and tastes. In the hands of a master like Friedkin, those sensations waft off the screen every time Joe ravages Dottie, cracks open a beer, or beats her family within an inch of their lives.

McConaughey slathers on all the snake-like menace he can muster for this pulpy, film-noir. He's Johnny Cash gone berserk, dressed in head-to-black duds with a blood-curdling sneer.

But the film's real casting surprise is 22-year-old Temple ("Atonement," "Notes on a Scandal"). Friedkin fought hard to cast the British up-and-comer as the film's sex slave, Dottie.

"The studio wanted me to consider two other actresses because of their box-office ‘heat'. But I knew I'd found Dottie the minute I saw Juno's audition tape," said Friedkin.

With the help of her little brother (who read Killer Joe's lines), Temple gave it her all on a homemade recording.

"Juno blew me away," said Friedkin.

"This girl, knock on wood, is going to have a real career in Hollywood."