After his sentence he returns to the streets and kills again. He is put back in prison and released again. One in ten death row inmates have been convicted of murder at least once. This means most have been convicted more than once and been given a chance to rehabilitate in prison and continue to commit violent crimes. Capital punishment is one of the oldest forms of punishment.
Most societies believe it is a fair punishment because it is portrayed in the Bible.
Colonists even used capital punishment before the United States was a country and most states continue to use it today. Capital cases are long and expensive and there is no proof that it deters crime. With some modifications, capital punishment could become cheaper and a lot more effective. If state governments used the death penalty consistently it could become more effective. In research, criminologists are forced to compare states that have the death penalty to those that hardly use it, which makes it almost impossible to learn from the research.