More than 30 years after the U.S. Supreme Court reinstated the death penalty, capital punishment remains an integral part of the American criminal justice system - at least in theory.

Thirty-six states have laws allowing executions, but only a few states carry them out with much frequency. New Jersey hasn't had an execution since 1963, and Pennsylvania, which has the fourth-largest death row in the nation, has put to death just three inmates during that same period, and all three essentially asked for it after giving up their appeals.

The question now, after New Jersey's historic move to abolish capital punishment, is whether other states will be propelled to take the same step, especially places such as Nebraska, Montana and New Mexico, where state legislatures have considered abolition but haven't had enough votes for passage.

"I think in those kinds of states, the arguments made in New Jersey will reverberate," said Richard Dieter, executive director of the Death Penalty Information Center, which tracks executions. He said Maryland and Illinois, which have moratoriums, were among other states to watch.

Montgomery County District Attorney Bruce L. Castor Jr. said he didn't think New Jersey's move would have much of an impact, especially in Pennsylvania, where 229 inmates await execution.

"I think most states are much more conservative than New Jersey and think that people who commit certain offenses deserve to be executed," Castor said.

Indeed, Gallup polls show roughly two of three Americans say they favor the death penalty, and 42 executions have taken place this year in 10 states, mostly in the South. Texas maintained its nationwide lead by putting to death 26 inmates. Oklahoma and Alabama each carried out three executions and Indiana, Tennessee and Georgia had two each.

But in the last few years, the number of death sentences has dropped, and the number of executions also has declined. Both decreases are attributed largely to scientific advances in DNA testing, which has become the great equalizer in the justice system because it helps convict the guilty and exonerate the innocent.

Since 1989, 209 defendants have been cleared by DNA tests, including 15 people sentenced to death, according to the Innocence Project, which works to free those wrongfully convicted.

In Pennsylvania, Nicholas Yarris spent 22 years on death row before he was cleared by DNA in a rape and murder in Delaware County. He is among an estimated 75 Pennsylvania inmates who have won new sentencing hearings or retrials after courts found serious legal errors in the way their original cases were tried.

James E. Coleman Jr., a law professor at Duke University who teaches about the death penalty and wrongful convictions, said the scientific advancements had exposed troubling problems in the reliability of the system, which has the public worried.

"There's now objective evidence both that the system is flawed and that judges and prosecutors and police make mistakes," he said. "I think the public doesn't want that."

Coleman said public support for the death penalty relied on assurances that death-penalty cases are fairly administered and reserved only for the most heinous crimes.

That's not always the case, he said.

"What we see in states like Pennsylvania, Florida and Texas is that it's like a lottery. It's not about how bad the crime is, but often how bad the lawyer was, or what county the crime occurred in," Coleman said.

DNA exonerations spurred a lot of the rethinking that is going on, especially within the justice system, where a growing number of judges, prosecutors, and law enforcement officials have begun over the last five years to voice opposition to the death penalty.

In New Jersey, the grass-roots organization New Jerseyans for Alternatives to the Death Penalty made slow but steady progress by highlighting not just the risk of executing the innocent, but also the high cost of death-penalty trials and appeals.

The group also focused attention on the plight of survivors of victims, who wait for years and years as the seemingly endless appeals play out, and enlisted the help of relatives of victims. Some former prosecutors also spoke out against the death penalty.

"New Jersey is providing the model of how it's done," said Sister Helen Prejean, who wrote the book

Dead Man Walking

, and who traveled across New Jersey to speak out against the death penalty.

David R. Dow, a law professor at the University of Houston who has been representing death-row inmates for 20 years, said he believed states with small death-row populations and those that don't often carry out executions might well be influenced by New Jersey.

But certainly not Texas, which he said would be "the last state" to ever get rid of capital punishment.

Dow said he didn't believe the U.S. Supreme Court would ever toss out the death penalty, as it did in 1972. If capital punishment is ever defeated, he said, "it's going to come from state legislatures, one at a time."

It won't be for moral reasons, he said, but for a more practical reason highlighted in New Jersey: the high cost of executions.

Europeans, meanwhile, will rejoice in what New Jersey has done. In Rome, the Coliseum, which Prejean described as the "oldest symbol of state killing" was due to be awash in lights to celebrate the abolition.

"The word will travel around the globe that there is a state in the United States of America that was the first to show that life is stronger than death," Prejean said.

Contact staff writer Emilie Lounsberry at 215-854-4828 or elounsberry@phillynews.com.