Thou Shall Not Kill. However, many secular arguments can also be made against the Death Penalty. It is more expensive. However, the cost of killing that same person is 2.3 million.
Race plays a role in the death penalty.
Money plays an important role as well. Many of those on death row are poor. They were not able to afford their own lawyer, and were assigned a public defendant. Often, these lawyers are not familiar with capital cases and therefore not effective counsel. The death penalty does not deter crime.