Because murder is so often a spur-of-the-moment act, Wick, even many death-penalty proponents don’t claim it’s necessarily a “deterrent.” (Though it’s sure as heck a deterrent to the convicted murderer.)
The penalty’s underlying principle is simple: Human life is precious–so precious, in fact, that if you take someone else’s, you forfeit your right to yours. In other words, you pay the ultimate price–just as you made your victim pay.
As for catching “the right” ones: We work toward a first-class justice system, with access to all necessary resources for everyone involved. Then, recognizing that no system devised by man will ever be perfect, we proceed to do the very best we can.
Why is this so hard to understand?