How about just following through with the executions instead of sitting on death row appealing until they die of old age. The threat of death isn't much of a threat when you know it's probably not going to happen. and if it does you are most likely going to spends many many years in prison where the roof over your head, the food in your belly, and your cable and gym membership is all paid for by someone else...before you are either nicely "put to sleep" like the family pet or die of old age.
Many nations have capital punishment and have very low crime rates because of it. They also have frequent mass killing of citizens and people are often taken right off the street and sold. Too bad people can't just care for one another.