Argument: Life in prison deters crime/murder as well as the death penalty
Archbishop Charles J. Chaput, "Justice, Mercy, and Capital Punishment", 2005 - "The Catechism of the Catholic Church explains it in these words: If 'non-lethal means [such as life without parole] are sufficient to defend and protect people’s safety from the aggressor [i.e., the convicted murderer], authority [should] limit itself to such means, as these are more in keeping with the concrete conditions of the common good and more in conformity with the dignity of the human person'. (2267). John Paul II, writing in The Gospel of Life, stressed that 'the nature and extent of the punishment [for capital crimes] must be carefully evaluated and decided upon, and ought not to go to the extreme of executing the offender except in cases of absolute necessity; in other words, when it would not be possible otherwise to defend society. Today however, as a result of steady improvements to the organization of the penal system, such cases are very rare, if not practically non-existent' (no. 56). In modern industrialized states, killing convicted murderers adds nothing to anyone’s safety. It is an excess. It cannot be justified except in the most extraordinary conditions."
Jack B. Weinstein, a Senior U.S. District Court judge in the Eastern District of New York, said in 2000. - There is no convincing statistical analysis showing it has any more deterrent value than life imprisonment. This is what you would expect since almost no murders are accomplished by people who calmly weigh the risk of against the possible benefits of whatever skullduggery they are involved in at the time they kill.
Terrence Hallinan, San Francisco District Attorney. "Call for California to Stay Executions". San Francisco Chronicle. 6 Jan. 2001. - The death penalty does not constitute any more deterrent than life without parole.»«[T]here's a moratorium on the death penalty in San Francisco during my administration. ... I am cognizant of what's happening all over the country, where people are questioning the fairness and appropriateness of the death penalty. I feel LWOP (life without parole) is a better resolution in those cases...