A recent Wall Street Journal Commentary declared that each execution resulted in 74 fewer homicides the following year.
A few responses from published in the WSJ illustrate the fallacy of the wild claims of the authors, one of whom purports to be a statistician. Interesting that this tidbit was published in the Wall Street Journal rather an a social science (read peer reviewed) source.
Let's clear the air. Numerous studies have claimed to show that the death penalty is a general deterrent only to fall victim to the examination of other social scientists who show various methodological flaws. Measuring what does not happen is a very difficult task.
On the other hand, we can show that the death penalty is no more or no less of an effective general deterrent than life in prison. Numerous studies exist to support this claim. Comparisons between states that do and do not have capital punishment, that abolish it, that bring it back all point to no statistically significant difference.
So we have lots of empirical evidence that a far less expensive and reversible alternative to capital punishment is available. Money squandered on pursuing a sentence is is rarely imposed and carried out is not sound fiscal policy.