Montie has it right. I would simply add that, to me, the best argument for the "death penalty" (assuming that it is applied in executions within a reasonable time of conviction), is that it actually provides a moral bottom line for a civilized society. By that, I mean that it recognizes that certain crimes are so absolutely horrendous and unacceptable that there is no possibility of some future second chance. Without it, there is always the possibility of some escape - either actual escape, exrernal destruction of a life-prison, future changes to the law (as in this article), a pardon, etc. Only the execution of people as epistemologically-certain-as-humany-possible of guilt in the truly heinous crimes draws a clear and certain line.