Just because a state or country makes it legal, doesn't make it right.
It makes it not murder.
The basic principle of murder is still being implemented.
Well then locking somebody up in prison makes it the same principal as kidnapping. But apparently that's allowed?
What is your point? The same thing can be achieved by sentencing someone to life in prison with no chance of parole.
Plenty of murders have killed and committed other violent crimes in prison. If they are dead, they cannot.
With a capital murder charge, they are normally segregated from general population.
If they are on death row, maybe. But usually most murderers are with the general population unless they prove themselves to be a danger to other inmates.