A recent article by Stephen Bainbridge in TCS Daily goes into some of the teaching of the Catholic Church on the death penalty, but does not really clarify things quite fully enough. For example, he says:

…the Catechism does not ban the death penalty per se. Instead, it leaves open room for the exercise of prudential judgment with respect to the question of whether, in a particular case, "bloodless means" will not be "sufficient to defend against the aggressor and to protect the safety of persons."

But that is not a sufficient summary of what is left up to prudence. For the Catechism also says:

Today, in fact, as a consequence of the possibilities which the state has for effectively preventing crime, by rendering one who has committed an offense incapable of doing harm – without definitely taking away from him the possibility of redeeming himself – the cases in which the execution of the offender is an absolute necessity "are very rare, if not practically nonexistent.

So, if someone should come up with a prudential judgment that all, or most, murderers should receive the death penalty, that would not be a legitimate use of prudence, since it would be a judgment radically at odds with the one that the Catechism teaches. The exercise of prudential judgment on this issue is thus not left wide open, but constrained by the teaching of the Catechism.

Bainbridge also says:

Cardinal Renato's pronouncements on Saddam's execution reflect his own prudential judgment, but they need not be regarded as Magisterial teachings to which the faithful are obliged to give religious assent. Instead, faithful Catholics may exercise their own prudential judgment on that issue.

Bainbridge's complaint as it relates to Cardinal Martino's pronouncements on the death penalty — where Martino had said that "no one can give death, not even the state"— is that it appears to contradict Church teaching. Now (putting aside the amazing issue as to whether Bainbridge is in fact accusing Martino of teaching against the Church, or merely coming up with some prudential judgment that Bainbridge happens to disagree with) we can look a little further into the papal encyclical Evangelium Vitae, where it deals with the case where someone may have to be killed as a matter of self defense:

Unfortunately it happens that the need to render the aggressor incapable of causing harm sometimes involves taking his life. In this case, the fatal outcome is attributable to the aggressor whose action brought it about, even though he may not be morally responsible because of a lack of the use of reason.

Where someone must be killed as a matter of self-defense (which is the only reason for capital punishment allowed by the Catechism), the outcome is not a choice that has been placed in the hands of the state, but something where choice has been taken away by the actions of the aggressor. So indeed, it is not up to the state to freely choose whether to give the death penalty or not, since it is the actions of the aggressor which may necessitate the penalty. The quote from Martino is quite defensible as a part of Catholic teaching.