What information and statistics do you have regarding the death penalty and very punitive sentences deterring crime?

My question grew out of this question which surveyed the collective whether we are in favor or against the death penalty.

Cruiser posted an interesting graph showing homocides decreasing during the years the death penalty was used more often than years it wasn’t. Of course we need to know what else was going on those years, it could simply be a correlation drawn and not the direct cause.

It seems to me countries like Singapore and Saudi, where they are extreme in their punishment of criminals from what I understand have less crime. At the same time countries who treat criminals with dignity, and have a rehab mentality also have low crime.

So, what is the best solution? Do the extremes work best, and the middle ground that seems to be the US is the least likely to be effective? I think crime in the US has more to do with the circumstances of life, rather than what the punishment might be. Although, maybe that is dependent on the person. Again going back to environment. Some people assume they will wind up in jail one day, while others would not fathom such a thought. So the threat of jail and punishment carries a heavier weight with the person who is more removed from the idea I think.