Interesting facts here on how the death penalty is a deterrent.
http://www.prodeathpenalty.com/DP.html
This was interesting...
Imposition of the death penalty is extraordinarily rare. Since 1967, there has been one execution for every 1600 murders, or 0.06%. There have been approximately 560,000 murders and 358 executions from 1967-1996 FBI's Uniform Crime Report (UCR) & Bureau of Justice Statistics (BJS).