I have a prisoner on death row with the cop killer trait. Once or twice a day, armed guards or dog handlers show up to beat him to death. The guards I have on patrol don't do anything to stop them. I know they'll beat him to death as I've had to reload several times; I don't want him to die before he's executed. I lock his door shut, but then he can't eat unless i manually open it. And when I forget, he gets violent and the guards are all too eager to kill him.

Any advice?

It's been a while since I played but can't you have his meals delivered to him?

He's on permanent lockdown, so his meals are delivered. The problem is the guards overreact to everything he does. Even after he's tazed or unconscious, they keep beating on him.

When he starts destroying things in his cell, guards come rushing from all over. It takes a lot of micromanagement to keep the guards away when he starts rioting. It's getting to the point I might stick him in rival gang territory.

The other DR inmate is a model prisoner, and I'll feel bad if he gets fried.

I haven't tried this yet (maybe tonight), but have you tried making a Protective Custody wing (for Snitches and Cop Killers)? I would try to give him a large room with complete stuff. Make the wing Staff Only and set the PC regime to Eat/Lockdown/Yard only. Try to put minimum guards/armed around this wing to lessen suppression.

I had a Cop Killer once before and I tried protecting him all I could. I think it's easier to handle if the prisoner don't have the Volatile/Extremely Volatile trait. Armed guards kept popping a cap on his ass. I had to let him go, he's a pain.