it is completely hypocritical to use the eye for an eye argument. killing prisoners has no benefit, other than to make some people feel better. therefore you're simply killing them for your own enjoyment.
the purpose of locking them up is to prevent them from doing it again, so by all means lock them up and throw away the key, but to do to them what they did to others is to become criminal and evil yourself.

ciao,
misterdavid