toughest custody challenges. run down and overcrowded facilities, the sky high number of gangs. >> this is the gang capital of the united states, if not the world. >> and an exploding mental health population. >> we are the de facto mental health system. >> now for the first time since a shocking scandal brought the sheriff's department under fire -- >> there are certain members of the sheriffs department who believe they're above the law. >> they're allowing one camera crew unprecedented access, ours. is your life in danger in here? >> yes. >> i love you, okay? >> it's heart wrenching sometimes to hear their stories. >> tonight i'm headed behind bars to discover what it takes to overhaul and run the country's largest jail system. >> the county jail is literally a beast. you can feel the tension, and it can be bad.