The death sentence for convicted Boston Marathon bomber Dzhokhar Tsarnaev was a legitimate use of state authority, even if Catholics may disagree with it, said a moral theologian in the nation's capital.

"We accept that the state has done its job, that this is the decision of the state which the state is morally free to make, according to the Church's teaching," Fr. Thomas Petri, O.P., dean at the Dominican House of Studies in Washington, D.C., told CNA.

"I think a Catholic response now is to pray for Tsarnaev, to pray that he repent, that he repent and come to the Lord."

Catholics were among the most vocal proponents of sparing Tsarnaev the death penalty. The 21-year-old former student at the Massachusetts Institute of Technology was convicted in a federal court for his role in the bombings that killed three and injured hundreds at the finish line of the 2013 Boston Marathon.

Sister Helen Prejean, a well-known Catholic activist against the death penalty who wrote the book "Dead Man Walking" about her experience ministering to a convict on death row, testified against capital punishment for Tsarnaev. She insisted after meeting with him that he was remorseful for what he did.

The Massachusetts Catholic bishops also advocated that Tsarnaev be spared the death penalty, saying in a statement that any threat he posed to society had been neutralized and that "society can do better than the death penalty."

They quoted a 2005 statement by the U.S. Bishops that "no matter how heinous the crime, if society can protect itself without ending a human life it should do so."

Recent months have seen increased discussion on the role capital punishment plays in society, if any.

Recent Popes have spoken about the matter. In a March letter to the International Commission against the Death Penalty, Pope Francis emphasized that in present times "the death penalty is inadmissible" and is "an offence against the inviolability of life" since the threat a person might pose to society has been neutralized with his being in state custody.

Pope Benedict expressed his hope that more countries will eliminate the death penalty at an international conference organized by the Sant'Egidio Community in 2011.

In his 1995 encyclical Evangelium Vitae, Pope St. John Paul II said that "the primary purpose of the punishment which society inflicts is "to redress the disorder caused by the offence'," quoting the Catechism of the Catholic Church.

He added that the state's punishment "ought not 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 in the organization of the penal system, such cases are very rare, if not practically non-existent," he said.

The Church has always taught that states have the authority to dispense justice – which includes the penalty of death when an offense is grave enough – Fr. Petri said, and recent Popes have not departed from this tradition.

"There's a very important nuance here that Catholics need to understand," he said, "which is that the Church's tradition and its magisterial teaching, which is unchanged by Pope Saint John Paul II, Benedict, and Francis, is that states and governments have the right to inflict the penalty of death when guilt is absolutely known and when the gravity of the crime rises to the death penalty."

And that prudential determination of when it must be applied is left to the state – in Tsarnaev's case, the jurors picked by the state to determine his guilt, the priest added.

The judgment is ultimately a prudential one, he continued, and this is clear even when John Paul II said in Evangelium Vitae that the need for capital punishment to protect society from offenders is "very rare, if not practically non-existent."

"Protecting society is not the primary purpose of punishment," he said. "The primary purpose of punishment is retribution, by which we don't mean revenge but by the society expressing its moral outrage, its outrage at the heinous gravity of a particular crime." It is here where "prudence" determines the proper response to an offence.

Thus, prudential application of the death penalty differs from support for intrinsic evils like abortion and euthanasia, he explained.

"So the death penalty, when, if, and how it is applied, is a matter of prudence for Catholics, which means that Catholics can in fact disagree with even papal teaching on this," he said, while also cautioning that "Catholics really need to take seriously" the papal teaching.

"But they're still free to say 'well I normally agree that we shouldn't be doing this, but in this case I can see why it would be merited'."

Then-Cardinal Joseph Ratzinger addressed this topic in a 2004 letter to Cardinal Theodore McCarrick of Washington, D.C.

After reiterating Church teaching that "abortion or euthanasia is a grave sin," Ratzinger wrote that "not all moral issues have the same moral weight as abortion and euthanasia."

"While the Church exhorts civil authorities to seek peace, not war, and to exercise discretion and mercy in imposing punishment on criminals, it may still be permissible to take up arms to repel an aggressor or to have recourse to capital punishment," he stated.

"There may be a legitimate diversity of opinion even among Catholics about waging war and applying the death penalty, but not however with regard to abortion and euthanasia," he added.

What is the role of a Catholic juror in such a case as the Boston bombing case? It's not entirely clear, Fr. Petri admitted.

Catholics opposing the death penalty on grounds of conscience were "effectively disqualified" from jury duty in the case, USA Today reported in April, since they from the beginning would not consider the possibility of a death sentence.

"Firstly, I think that if they feel convicted in conscience that they can't vote for the death penalty, then that is a moral duty not to," Fr. Petri said.

However, whether the Church permits or prohibits Catholics from voting for the death penalty on a jury "is not as clear," he continued, and even if the Church actually does not permit it, "it's not being taught and therefore Catholics will not be culpable for voting for the death penalty."