Archbishop Oscar Romero was slain in San Salvador by a right-wing death squad nearly four decades ago as he celebrated Mass in a hospital chapel. Now, Salvadorans and human rights activists say they have reason to hope his killers may be brought to justice.

Authorities in El Salvador reopened the moribund investigation into the case in mid-May. Less than a week later, Pope Francis named José Gregorio Rosa Chávez — a close collaborator of Romero — as El Salvador’s first-ever cardinal, an act buoying belief that the truth about the 62-year-old archbishop’s assassination finally could be presented in a Salvadoran court.

Yanira Chacon, a church outreach worker at St. Brigid’s parish in Westbury, said when she first heard the case was being reopened, she thought, “Thank God, hopefully we will come to a closing, not only for me but for all the Salvadoran people, of knowing exactly what happened and who and how and why.”

Rosa Chávez, 74, was scheduled to arrive on Long Island on Thursday night for a three-day visit. It is his first trip to the United States since Francis made him a cardinal, elevating him from auxiliary bishop to one of the highest positions in the Catholic Church. He was ceremonially installed in June.

He is visiting the Island both for the community to celebrate his new position and to provide solace to Latinos shaken by gang murders and an immigration crackdown, according to Bishop John Barres, spiritual leader of Long Island’s 1.5 million Catholics.

The cardinal’s presence — and his ties to Romero, now one step away from being made a saint by the Vatican — hold deep significance here, where an estimated 100,000 Salvadorans are among the top five concentrations in the nation.

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No one ever has been charged or convicted in El Salvador for Romero’s killing. In a civil case in California in 2004, one of the alleged leaders of the plot who was living in the United States, Capt. Alvaro Saravia, the former security chief of the rightist party ARENA, was tried in absentia, found guilty and ordered to pay $10 million to a relative of Romero.

Some of the alleged assassins and their alleged financial backers from El Salvador’s oligarchy are dead, but others survive, according to human rights lawyers.

Reopening the case is “a very welcome sign,” said lawyer Matt Eisenbrandt, author of “Assassination of a Saint: The Plot to Murder Oscar Romero and the Quest to Bring His Killers to Justice.”

“But now we need to see some political will by the prosecutors and the Salvadoran government to make sure the prosecutors have all the resources and support they need,” said Eisenbrandt, who helped locate Saravia in Modesto, California, at the time of the civil suit.

A spokesman for the Salvadoran Embassy in Washington did not respond to a request for comment on why no one has been charged in the slaying.

El Salvador was wracked by a 12-year civil war from 1980 to 1992 between leftist guerrillas and a right-wing government and military that eliminated priests, nuns, campesinos, teachers and others viewed as subversive, according to a 1993 Truth Commission report sponsored by the United Nations.

Some 85 percent of the 75,000 victims in the war were killed by the military or other state agents, the commission found. The Salvadoran government at the time disputed the report, calling it unfair, and immediately passed an amnesty law aimed at those named in the Truth Commission.

The administration of President Ronald Reagan had backed the government during the 1980s with at least $1 million a day in aid, stating it was trying to stop a Communist tide in Central America and that the human rights situation was improving.

Romero was known as the “voice of the voiceless” for denouncing government repression against the urban and rural poor. He was shot and killed by a sniper from a right-wing, military-affiliated death squad on March 24, 1980, as he raised the chalice during Mass in the chapel of a cancer hospital.

The assassination unleashed an era of state-sponsored terrorism that included the slayings of four U.S. churchwomen in December 1980 and a 1981 massacre in the village of El Mozote, where an estimated 1,000 people — 250 children among them — were killed by an elite, U.S.-trained Army unit, said Terry L. Karl, a Stanford University professor who served as an expert witness in the California case.

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In 1989, she added, the same military unit that carried out the El Mozote massacre killed six Jesuit priests, their housekeeper and the housekeeper’s daughter on orders from their superiors.

The Romero killing “was the single most important act to plunge El Salvador into civil war,” Karl said.

“I think what they were trying to accomplish was to show that if you can kill the archbishop, you can kill anybody,” she said. “When you can kill somebody like him, with his stature, and get away with it, and kill him in church while he is saying Mass, and while he is offering the blood and the body of Christ, what you are really saying is no one is safe.”

“It was really to instill terror,” she said, “and it did.”

Judges were too afraid to investigate the Romero murder seriously during the war, she said, and later the 1993 amnesty law shut down attempts to pursue most cases.

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But the law was repealed last year by the country’s Supreme Court, opening the way for prosecution of notorious crimes in the tiny Central American nation. A prosecutor also has opened an investigation into the El Mozote case, which took part in Morazan, the home state of Rosa Chávez and of many of the Salvadoran immigrants on Long Island who fled the horror.

Karl is among those who hope that Rosa Chávez will press for a resolution in the Romero case.

He “surely supports justice for the victims of El Mozote and for Romero himself,” she said. “His voice, as a cardinal, is essential if El Salvador is ever to achieve the rule of law and the end of impunity.”

Some of the human rights groups that have pursued justice for years are cautiously optimistic that the time may be at hand.

Dixon Osburn, executive director of the Center for Justice and Accountability, the San Francisco-based group that won the California lawsuit, said, “It is a travesty that there has been no justice for decades.”

El Salvador “has not done what it needed to do to address the atrocities of the past,” he said. “That’s why this moment is so crucial.”

Chacon was at Romero’s funeral on March 30, 1980, when gunfire erupted amid the crowd of 250,000 people in the country’s capital city, killing at least 30. Witnesses said government-backed soldiers were behind the violence.

Of the cardinal, she said this week, “My hope is he will be supporting the group of lawyers working on it to finally bring justice to this case.”