Last time, it was Timothy McVeigh.

The death-penalty debate enters the headlines from time to time because of a notorious case. But even when a killer guilty of thousands of deaths was the one on death row, public opinion surged against the death penalty.

Now Scott Peterson has put the death penalty in headlines again.

Peterson, of course, is convicted of killing his wife Laci and unborn son Connor. And even though Peterson's conviction was literally celebrated by many Americans, when the question changed to whether or not he should be executed, polls again show America at a crossroads. Execution is running about even with life in prison without parole as Americans’ preferred way to deal with murderers.

That more people oppose the death penalty is good news to Catholics. The Church teaches that the cases when the death penalty should be used are practically non-existent in modern society.

The Pope has made this teaching normative in every way he can. He wrote it into an encyclical, giving it the greatest weight possible. Since encyclicals are regarded as part of the ordinary magisterium, the Catechism of the Catholic Church had to be changed after that, and it was.

As if to show how seriously he meant his teaching on the death penalty, the Pope took the next logical step. He vigorously opposed particular executions all over the world, appealing directly to civil authorities to spare the lives of the condemned.

But if the death-penalty opposition of the magisterium is clear, Catholics who argue about the death penalty often muddy the waters.

Abolitionists act as if the case against the death penalty is a simple application of the fifth commandment, “Thou shall not kill.” They even call the death penalty “murder.” It couldn't possibly be as simple as that, because in the same biblical passage in which God gives Moses the Ten Commandments, he singles out crimes deserving death. The Church doesn't take the abolitionist position.

But if abolitionists often get it wrong, so do Catholics who favor the death penalty.

They make convincing arguments about its justice, and even its teaching power. They say the death penalty is the state's way of saying, “Lives matter — they matter so much that when you snuff out the image and likeness of God in another, you forfeit your own life.”

But if that's what the state is saying, the public isn't getting the message. Read any article about a particular execution and you'll find what most people want from capital punishment: They want to do ultimate harm to the condemned.

Pope John Paul II puts the debate into a bigger picture of what's happening in our world today. He says our age's blindness to the value of life has created a “culture of death.” In such a culture, executions are bound to look like just another example of killing being used to solve a problem.

Instead of teaching the importance of life, capital punishment in our day simply becomes another part of the culture's anti-life ethos.

Death-penalty defenders argue that the Church's position as he states it is something new, and is at variance with Catholic tradition. It isn't. “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,” says the Catechism. “If, however, non-lethal means are sufficient to defend and protect people's safety from the aggressor, authority will limit itself to such means.”

And, after all, there's an even more ancient tradition — the tradition of mercy. This tradition goes all the way back to Cain and became part of the Church's urgent message in the 20th century. The Church called for mercy in official pronouncements about the Sacred Heart and divine mercy, and in popular devotions like St. Faustina's.

Catholic literature took up the theme as welll. J.R.R. Tolkein's wildly popular trilogy was a 20th-century Catholic's parable about mercy. Tolkein made the existence of the world he created in The Lord of the Rings hinge upon the mercy shown to the murderous Gollum.

Now, in the violence of the 21st century with its terrorism, war, abortion and ethnic cleansings, it's time for Catholics to start applying those lessons.

In an age that has forgotten the value of human life, we'll be surprised how much good our fidelity to the Church's teaching about mercy will do.