Insider Facts From Criminal Minds, 'Internal Affairs'

Going south!

1. Going south!

After two undercover DEA agents are murdered and a third goes missing, the BAU joins the NSA to investigate whether an underground Internet drug syndicate is involved. Also, Hotch hopes the team's work with the NSA brings them closer to finding the "Dirty Dozen" hitmen ring, on "Internal Affairs."
Club quarters

2. Club quarters

The art department went to great lengths to create a private gentlemen's club for this episode. It was inspired by the Diogenes Club featured in several Sherlock Holmes stories.
Passing for El Paso

3. Passing for El Paso

Acton, California served as El Paso, Texas in this episode. Scenes at the UnSub's farm were largely shot in Esperanza Valley over the course of 12 hours.
Shattered glass

4. Shattered glass

The realistic special effects in this week's episode were courtesy of Andre Ellingson and Tom Seymour, whose credits include Pirates of the Caribbean, Rush Hour 2, and plenty of Criminal Minds episodes.