WASHINGTON — When Boston Cardinal Sean O'Malley was asked at a news conference at the U.S.-Mexico border about how to persuade people to support comprehensive immigration reform, he pointed for an example to the Catholic Church's decades-long efforts to shift opinions about the death penalty.

"There was a time when Catholics were very pro-death penalty," Cardinal  O'Malley said April 1. Then Blessed John Paul II made a strong push to include opposition to capital punishment as a part of a consistent pro-life approach, he said. Activists took on the task of changing minds and hearts.

Today, support for the death penalty overall has dramatically declined. So have the number of executions and death sentences. But it has been a lengthy process.

The Catechism of the Catholic Church officially issued in 1992 said that although there may be circumstances that allow for such a drastic punishment to protect the public, "if bloodless means are sufficient to defend human lives ... public authority must limit itself to such means, because they better correspond to the concrete conditions of the common good and are more in conformity to the dignity of the human person."

In modern society, circumstances that justify capital punishment "are very rare, if not practically nonexistent," the catechism says.

Particularly in the 1990s, efforts focused on getting people past the notion that only "an eye for an eye" could constitute justice. Sister Helen Prejean, a Sister of St. Joseph, helped capture the Catholic imagination with her 1993 book about her experiences with death row inmates and the book-based 1995 movie "Dead Man Walking," for which actress Susan Sarandon won an Academy Award.

In addition to Sister Helen, a speaker's circuit grew. It now includes murder victims' families, exonerated former inmates, prosecutors, law enforcement officers and others with personal experience of the emotional roller coaster of capital punishment that put them on the side of abolition.

As Cardinal O'Malley observed, people began to see that the death penalty is not what they thought it was.

Now, Catholics are less likely than most Americans to favor the death penalty.

Data released in April from a poll last year for the Pew Research Center bears this out. Among all Catholics, 51 percent say they support capital punishment for those convicted of murder. A dramatically smaller percentage of Hispanic Catholics, 37 percent, support it.

Americans overall favor the death penalty by 55 percent, down from 78 percent in 1996, according to Pew's survey.

Karen Clifton, executive director of the Catholic Mobilizing Network to End the Death Penalty, said majorities of younger Catholics as well as Hispanics are likely to oppose capital punishment.

She said that recent Hispanic immigrants, for example, are from countries without capital punishment. When they come to the United States, some tend to accept it as part of the American way of life. "But when we come at it with the pro-life theology, it makes a big difference" in swinging people's views against the death penalty, she said.

The possibility that some on death row might be innocent also resonates  with people, Clifton said, as does data showing how arbitrarily death sentences are imposed. The rate at which prosecutors seek the death penalty and the rate at which executions are completed varies dramatically from one jurisdiction to another, even within one state.

The Death Penalty Information Center reports that in 2012, nine counties  in five states accounted for 35 percent of the death sentences. Fifteen counties in four states account for 30 percent of the executions in the United States since 1976, although they represent less than 1 percent of the total number of counties in states with the death penalty.

Nationwide, the number of executions has steadily declined since a peak  of 98 in 1999. There were 39 in 2013 and, as of April 17, there had been  17 in 2014, with another 13 scheduled. Several executions set for 2014 have been stayed. Many of those stays revolve around the availability of the lethal drugs used in executions.

Clifton said the complications of finding the lethal drugs for executions -- both legal and logistical -- represent a significant area of effort for opponents of capital punishment. European manufacturers of one of the main drugs used for years in lethal injection have blocked its export for execution. States are experimenting with new drugs, sometimes resulting in poorly managed, painful executions.

Meanwhile, organizations of physicians, nurses and anesthesiologists have said their members should not be involved with executions for ethical reasons.

Clifton said the Catholic Mobilizing Network is drafting a letter on the subject of lethal injection.

Amid this, retired Supreme Court Justice John Paul Stevens has a new book, in which he proposes adding a few words "such as the death penalty" to the Eighth Amendment. It would read: "Excessive bail shall not be required, nor excessive fines imposed, nor cruel and unusual punishments, such as the death penalty, inflicted."

In his "Six Amendments: How and Why We Should Change the Constitution," Stevens said that "the question that cannot be avoided is whether the execution of only an 'insignificant minimum' of innocent citizens is tolerable in a civilized society."

He wrote that he now sees the availability of life imprisonment without chance of parole as a viable means of preventing further crimes and deterring others from committing them.

"When it comes to state-mandated killings of innocent civilians, there can be no 'insignificant minimum,'" he said.

With a series of rulings in the late 1960s and 1970s, the U.S. Supreme Court sent states back to the legislative drawing board. Death sentences  and executions were suspended while states rewrote laws to adapt to rulings on proportionality of sentence to crime, arbitrariness, and on what constitutes cruel and unusual punishment.

Currently, 32 states and the federal government have capital punishment  on the books; 18 states and the District of Columbia have outlawed it. Eighteen states and the federal system have had no executions in at least five years.

Supreme Court rulings in the past 20 years have not tackled the overall constitutionality of capital punishment, but have limited its application to people with mental illness, mental retardation and who committed their crimes as juveniles.

New Hampshire was poised to be the final state in New England to outlaw capital punishment before an April 17 tie vote in the Senate meant an end to the effort for this legislative term. The House had voted more than two-to-one to end the death penalty and Gov. Maggie Hassan had said she would sign the bill. The state has just one person on death row and its last execution was in 1939.