. >> in her 15 years at corcoran, officer diane murphy has learned just how powerful prison gangs are. >> when you come to the prison, you have to join a gang. you have no choice. if you don't join a gang, well, you better pack up and go to the sergeant's office and tell him you are ready to leave the yard, because there's no options. you have to be in a gang. >> within these fiercely guarded activities, the most innocent active become life-threatening in a moment. >> you are run, a man walking out in front of you, you want to yell out track, because he is liable to proceed behind you and nail you, either with a weapon or a fist. >> somebody want to control this basketball court or that basketball court or this weight bench or that weight bench. the cos having in to do with that, that is amongst the inmates, the convicts. sometimes you be able to talk it out and get it settled without violence. sometimes you have to bring violence. this is just like on the street, you can be here today and you can be gone tomorrow. >> violence always on the verge of exploding, the officers are as much