The Vatican characterized the event as "tragic" for two reasons. The first is familiar as the current Church teaching applied in all such cases: capital punishment is no longer justified today because other means of preventing further aggression by killers like Saddam are readily available. The second is that his execution is likely to arouse emotions that will only make the current strife in Iraq worse. I tend to agree, even as one who was happy to see Saddam and his evil regime come a cropper. (That's a separate matter from the question whether the post-Saddam era should or even could have been handled better; the question of the war's justice hinged on that other question, and things aren't looking good right now.) It may well be that more death will result from executing Saddam than would have from letting him spend his waning years in prison. But we need to be careful here. This is not simply a matter of reciting the catechism.
To be sure, Catholics as such are bound in conscience by the following teaching:
Assuming that the guilty party's identity and responsibility have been fully determined, the traditional teaching of the Church does not exclude recourse to the death penalty, if this is the only possible way of effectively defending human lives against the unjust aggressor.
If, however, non-lethal means are sufficient to defend and protect people's safety from the aggressor, authority will 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.
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 non-existent." 68
If one construes 'incapable of doing harm' narrowly, to apply only to the convict's physical actions, then the Vatican is right to condemn Saddam's execution as unnecessary for the public good. But there are cases where one might and even should construe that phrase more broadly. One can think of captured people, typically terrorists, dictators, and warlords, who are more dangerous alive than dead because, as long as they remain alive, their followers might not shrink from fighting for them and even from fighting to spring them. It's doubtful that was the case with Saddam, which is why I incline to agree with the Vatican's judgment in this case. But there doubtless can be, and may even be, relevantly different cases in which society is much safer with the perp dead than alive. If and when there are such cases, the death penalty is justified. I'm not asserting that there are such cases right now. I don't know. But Catholics as such are not obligated to believe there aren't and won't be any. That is a matter of empirical judgment, and the Church neither enjoys nor claims infallibility in such judgments.
The other thing to consider is that Saddam quite possibly was enabled to "redeem himself" by the way his sentencing must have concentrated his mind. In a letter he is said by his lawyer to have written on November 5, the day of that sentencing, he wrote: "I call on you not to hate because hate does not leave space for a person to be fair and it makes you blind and closes all doors of thinking..." He also was clearly making preparations to meet his Maker. Such things indicate that he might, just might, have begun to repent. I don't think he would have been even mildly inclined to do so if he had not been sentenced to death. With other trials pending, his harangues and theatric protests would simply have gone on for years.