The BAU is the new black.

On Wednesday's Criminal Minds, the BAU heads to a Texas prison after two guards are killed. Naturally, the primary suspects will be the incarcerated men, but how to narrow down the pool of hundreds? Leave it to Reid (Matthew Gray Gubler), of course. As seen in the sneak peek above, he takes approximately 126 minutes to go through prisoner files and finds one unaccounted for.

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The episode was directed by Thomas Gibson, his fourth stint behind the camera and second this season. But this one is unlike the rest in that the majority of the hour is confined to one location, the prison.

"There's one option to get a prison in Los Angeles, which is an old women's facility that the county sheriffs own, and they use it partially for storage and training and shooting," Gibson tells "We've shot there before and you have to book it way in advance. It's really appropriately bleak. Our art department could create a prison, but it's better to go there."

Being in an actual prison not only captured a far more realistic atmosphere, but the claustrophobic feel Gibson was going for. "The whole idea [was] to feel like we were shut in with everybody for as long as it took to figure out what was going on," he says. "I wanted it to have the feeling that everybody was watching everybody else, and I think you definitely get that in a few places that benefits the story. There are few fight scenes and one big fight scene ... where I made a last-minute switch [to shoot in] a larger exterior room before the fight happens. It was a good call, I think. But it's pretty grim being there. We ended up needing only four days there. Four days in prison is more than enough!"

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

(Full disclosure: is owned by CBS.)