Oh yes, and the prisons are FULL of people who really didn't do it, and the "real" killer/molester/burglar is out there SOMEWHERE.
Inmates lie. They lie about their crimes, they lie about mundane bullcrap, they lie about big stuff.
Do inmates sometimes get brutalized? Sure. Usually by other inmates, sometimes by corrections officers. Does it happen all the time? Hardly. Inmates like to self-harm, hoping to get someone else into trouble, or to get out of something.
Corrections officers have a tough job. They have to deal with the dregs of society on a regular basis. They're spit at, have feces and urine thrown at them, have other bodily fluids flung at them, they're threatened on a daily basis, and hell, inmates try to kill them. It's too bad you'd prefer to think the worst of them.