Exclusive Criminal Minds Sneak Peek: Can People Be Turned into Killers?

Can you be an innocent victim but also the red-handed killer?

That's what Criminal Minds is asking on Wednesday's episode. After a string of people claim they were attacked at home by a clawed monster - dubbed Mr. Scratch (the episode title) - before finding their loved ones dead, the BAU has to break some bad news to the victims: They were the killers. (Watch a sneak peek above.)

Finale preview: Get the scoop on all your favorite shows

"When Breen [Frazier, the writer] pitched the teaser, I was like, 'I'm in!'" executive producer Erica Messer tells TVGuide.com. "You've got victims who are also killers. That, to me, is such a cool way to do a Criminal Minds episode. Leave it to Breen to come up with something like that. We're always looking to do something different and to me, that was different. It's a psychological thriller because these people feel remorse. They aren't killers in their nature at all, but they've become them. So the question is, how did that happen and who was the mastermind behind that?"

The masterminds behind the episode were Frazier and Matthew Gray Gubler, who stepped into the director's chair for the eighth time. "Matthew once again delivered an amazing masterpiece of what we call the Gubler Episodes," Messer says. But this time, the actor did more than just pepper the hour with his usual eerie, weird, less-is-more flair. He also played the unsub! "I'm happy to give this away: I played Mr. Scratch," Gubler says of the talon-wielding, reedy shadow monster. As was the case with his previous directorial efforts, when he did his own artwork to fit his vision, Gubler was talked into donning the DIY costume for the titular creepazoid, who is only seen in shadow.

Season MVPs: What were the year's best performances?

"I had gone to great lengths to find the right actor with the physicality [and] a thin, spooky choreography to them. And my assistant director finally just said, 'When are you just gonna admit that you're playing Mr. Scratch and stop this farce of looking for someone else? You know you're gonna play it, I know you're gonna play it, so just put on the outfit,'" he says. "For one of the scares, we had to dress up the cameraman, Darcy Spires, as Mr. Scratch because he was the one casting the shadow. ... I was wearing a skintight black bodysuit, a long commedia dell'arte mask and a cardboard beak that I had made at home, and then these incredible hands that were crafted by our effects department team that were actually made out of tinfoil. If you saw me on set, it looks like I'm about to go to the most ridiculous Halloween party of all time dressed as some sort of Renaissance faire man."

Which obviously means we all need to see the full costume in all its glory after the episode airs, right? "I might do that. But then it's really anticlimactic because it's not scary at all! It'll ruin it!" Gubler says with a laugh. "The shadows are more scary. I think if you don't see it, it's always better. I try to put the audience in the scariest seat of the house for every single scene. The episode is such a haunting thought -- you, an innocent person, can be turned into a serial killer -- and it's haunting all the way through the end."

Criminal Minds airs Wednesdays at 9/8c on CBS.

(Full disclosure: TVGuide.com is owned by CBS.)