Let me narrate this as an insider before you watch this YouTube video below.
The 5 inmates you see talking by the door is indeed a trial by the Inmate Council. The man who was attacked was probably sentenced to a beating for not fighting when challenged. Refusing to fight is a criminal offense in jail.
Notice that the inmates, not the guards determine these things. This is "jail" not a maximum security prison, yet the prisoners are neglected to the point of creating their on ad hoc government.
Notice that a non-violent person who stole a car (probably to support a drug habit) is housed with an Aryan Brotherhood enforcer who, in this case, has been chosen by the local inmate council (probably without knowing this man's true violent history) as their local enforcer (its a volunteer position). Normally, a beating in jail is just that. But the enforcer in this case isn't your normal jail resident, but an extremely violent man housed with a population of local Maricopa County residents.
I spent 3 weeks in a cell block like this. The entire atmosphere is filled with tension. Notice that everything in this room will hurt you. Everything in here is steel and concrete (except for a thin piece of foam for a mattress which in the lower bunk is resting on a slab of concrete). Dying in this environment is easy to accomplish without a beating. People's bodies aren't designed to compete with materials so tough they would smash a car.
Notice the small enclosures of the cell. In the cell block I was in, which house 2 prisoners in this size room, the top bunk is about 5-1/2 feet from the floor with no railing or ladder to climb into it. I tore my rotator cuff just trying to get into and out of the top bunk in a cell like this. There are stories of people falling out of the top bunk and rupturing their spleen, dying from a blow to the head from the toilet (a stainless steel fixture just out of sight on the camera), and breaking limbs.
Notice that there are no guards about and no one watching the surveillance cameras. This is very typical. Inmates can smoke cigarettes, take drugs, fight, and do almost anything they want (as long as they follow the Inmate Council's rules). Guards are chatting, talking on the phone, or just not visibly there. This is one reason I say that the employees are the most dangerous people in the jail. In this one incident, none of the 3-5 guards saw anything. These guards are stationed in a "bullet-proof" glass enclosure high on the far wall and level with the top row of cells and above the steel tables shown on the floor below. If the inmate falls, hits his head, has an epileptic seizure, or drops into a diabetic coma, they will probably die if not for other inmates yelling at the guards to get their attention. This is a graphic example of the poor training, lack of supervision, and mismanagement I speak about.
If you replay this video, you will notice that even when the guards to run inside, when they reach the fallen prisoner, they just mill about over the body. No CPR, no first aid of any kind, nothing to attempt to save the man's life. They simply have no idea how to respond to an injured prisoner other than to make a radio call for someone to come to help, which can take up to half an hour.
Lastly, murder is not a normal occurrence in this jail. Death by accident, neglect, and medical issue complications is far, far more common. This unusual incident happened because a violent man accused of murder was housed in an open doom. The idea of "Maximum" and "Minimum" security is a farce as far as I can tell. If you've had a loved one in this jail, they could easily have been in that cell block. People are lumped where ever a bed appears and stay there until some incident (such as this) forces the jail employees to take some sort of action.
If Arizona sells its prisons to the for-profit prison industry, you can expect this type of occurrence on a much larger scale. It has already happened numerous times in other states.