Put yourself in the guards shoes. What would you do? Most of those guards are just like you and I. Several people in my family are or have been prison guards at the state penitentiary near where I live. I believe they might release some but most of the inmates would probably be shot and rightfully so. Think about this. Most of the guards at any facility live relatively close to the institution they work in. If they pick and choose who to shoot there very well could be an inmate left alive that watched a guard shoot a friend. What’s to keep that inmate from seeking revenge once he gets free. The inmate may not know where the guard lives but as he wanders away to try and go home, what if he does stumble across the guard. It’s not worth the risk. It is another one of those questions that is pretty much impossible to answer unless you are in that moment. As much as I hate to say it they should all be shot even though some “innocent” people may be killed. Better safe that sorry. I also think it would be easier to deal with emotionally if you shot them all as apposed to playing god and deciding who lives and dies.