Is it the episode with the 333 killer? And what is he doing with the lasers?
Edit: Just saw the episode. The bad guy takes the main detective guy prisoner, and has him sitting in a chair with various green lasers forming a grid around him. He has a gun on a tripod aimed at the detective which will go off if the lasers are passed, and a shotgun aimed at the door to the room that will go off if one of the lasers is passed. It was pretty cool