"..and how you would feel if some of these prisoners were killed and then found to be absolutely innocent at a later date?"

Okay so you lock someone up for life....they spend 25 years eating rat meat and bugs, getting gang raped in the shower, being beaten, robbed, abused and cheated of every day of their lives....then you find out they are innocent, how do you give them their lives back? How can you take that back? You can turn them loose, you can give them money, but you can never give back what you took from them any more than you can raise the dead.

Strikes me the best thing is not to make mistakes.