First, the death penalty is good public policy. The bishops argue that in “modern times the state can incarcerate those convicted of a capital crime for the rest of their lives-with no chance they will ever join society.”  This is false. In modern times, violent criminals who remained in prison do indeed routinely kill again. For example, in 1981 Donna A. Payant, an officer in the New York State Department of Corrections, was brutally murdered by inmate Lemuel Smith. Smith was serving two life sentences for murder. If he had been executed, Donna would not have been murdered.  Further, in the U.K. it was recently reported that “nearly 30 killers released from jail have gone on to kill again on Britain’s streets in the last decade.”  The bishops argue that the “application of the death penalty can be irreversibly wrong” because innocent persons can be executed. However as illustrated above, the failure to apply the death penalty can also be “irreversibly wrong” if murderers who are not executed murder again.
Second, according to the traditional teaching of the Church, legitimate civil authority has both the right and duty to punish deliberate murder (and other grave crimes) with the penalty of death. The Roman Catechism states:
"Another kind of lawful slaying belongs to the civil authorities, to
whom is entrusted power of life and death, by the legal and judicious
exercise of which they punish the guilty and protect the innocent.
The just use of this power, far from involving the crime of murder, is
an act of paramount obedience to this [the Fifth] Commandment
which prohibits murder. The end of the Commandment is the
preservation and security of human life. Now the punishments
inflicted by the civil authority, which is the legitimate avenger of
crime, naturally tend to this end, since they give security to life by
repressing outrage and violence. Hence these words of David: In the
morning I put to death all the wicked of the land, that I might cut off
all the workers of iniquity from the city of the Lord." 
Thus permitting the application of the death penalty in California as the ultimate punishment for the gravest crimes is both good public policy and in harmony with our Catholic faith. For these reasons, we urge Catholics to vote no on Proposition 34.
 Los Angeles Times, “California death penalty foes to try for ballot initiative”, August 26, 2011.
 See: http://www.cacatholic.org/index.php/issues2/reverence-for-life/death-penalty/538-prop-34-support
 New York Times, “Two-time murderer accused of killing a prison guard”, June 7, 1981.
 See: http://www.telegraph.co.uk/news/uknews/law-and-order/7147662/Killers-freed-to-kill-again.html.
 See: http://www.cin.org/users/james/ebooks/master/trent/tcomm05.htm.