Granted, a number of these nations also have stricter controls on firearms than we have in the United States. However, it seems reasonable to assume that if the argument that capital punishment is an effective deterrent to crime were valid, then there wouldn't be such large discrepancies in our crime rates. While criminals wouldn't have guns, they'd still be more inclined to commit crime since they'd know that doing so would not have dire consequences. But setting the deterrence question aside, there's an even bigger reason why the death penalty should be considered inappropriate in any case. Killing people is wrong, period.
Capital punishment is little more than state sanctioned murder.
It doesn't send the message that all human life is sacred and should be respected. It sends the message that murder is O.K. as long as you're in a position of high enough authority. Capital punishment is not the way to solve this country's violent crime problem. The entire judicial system needs an overhaul. It shouldn't be possible for repeat offenders, rapists and murderers to get out of prison on parole.