Former Nazi SS officer Erich Priebke enters the military court in Rome on Dec. 7, 1995. Priebke, a former Nazi SS captain sentenced to life in prison for his role in one of the worst atrocities by German occupiers in Italy during World War II, has died. (Domenico Stinellis/AP)

Erich Priebke, a former German SS officer who helped carry out one of the worst massacres in Italy during World War II and whose trial years later became a defining moment in Italy’s struggle to reckon with its wartime past, died Oct. 11 in Rome. He was 100.

The Italian newspaper La Repubblica reported his death, citing an announcement by Mr. Priebke’s lawyer. The cause was not disclosed.

In Rome, two sites have come to represent the battles and brutality that wracked the city and country during the war: Via Rasella, a street not far from the Trevi Fountain, and the Ardeatine Caves, on the outskirts of the capital. Their significance in Mr. Priebke’s life became public five decades after the war, when ABC’s Sam Donaldson confronted him on camera about the following history:

Mr. Priebke was second in command at the Gestapo headquarters in Rome on March 23, 1944, when a bomb exploded in Via Rasella and killed as many as 33 Germans marching along the street. That incident — a spectacular attack in the anti-Fascist campaign waged by Italian partisans — enraged the highest ranks of the Nazi leadership. Years later, Mr. Priebke said that Adolf Hitler personally responded with the order to execute 10 Italians for every German killed.

Nazi troops in Rome, whose commanding officers included Mr. Priebke, exceeded that demand. During the next 24 hours, they trucked 335 Italian men and boys out of the city and called them five at a time into the Ardeatine Caves, where, by candlelight, they shot the victims in the back of the head.

Other atrocities claimed more Italian lives. More than 500 died in the massacre in the Tuscan town of Sant’Anna di Stazzema, an incident that received renewed attention in the United States with James McBride’s 2002 novel, “Miracle at St. Anna,” and the subsequent Spike Lee film with the same title.

But no mass killing in Italy was as methodical as the slaughter at the Ardeatine Caves, said Alessandro Portelli, author of “The Order Has Been Carried Out,” a definitive account of the massacre and its transformative effect on Rome. Mr. Priebke admitted to killing two of the victims and checking off the others’ names as the troops led them in.

“It really is the symbol of the violence of the Nazi occupation,” Portelli said.

Tracked down in Argentina

After the war, Mr. Priebke escaped from a British POW camp and emigrated to Argentina, where he ran a delicatessen and led a German-Argentine cultural association. He did not attempt to disguise his identity. When the ABC television crew approached him in the early 1990s, Mr. Priebke did not appear surprised. Yes, he had been in the Gestapo in Rome in 1944, he told Donaldson, and, yes, he was present when the executions began.

“I feel very bad. Nobody from us wanted to do that,” he told Donaldson. “At that time, an order was an order. . . . I was a Nazi and young man. . . . Many young men do things when they are old men like me; now they are very sorry about it.”

With that report, Mr. Priebke’s private life in his idyllic Andean town came to an end. Days later, when Italy moved for his extradition, he was placed under house arrest. In November 1995, after the Argentine Supreme Court rejected his bid to remain in the country, Mr. Priebke found himself back in Rome.

So began years of legal wrangling that, like many war crimes trials, showed the difficulty of fitting history into the four walls of a courtroom.

The first complaint about the trial was that it took place in a military court. Many Italians considered Mr. Priebke’s alleged offenses worse than violations of an austere military code.

Then came a series of interruptions, including charges by the prosecution that judges were biased in favor of Mr. Priebke and an apparent escape attempt by Karl Hass, another former Nazi who was set to testify.

Rancor surrounding the trial climaxed with a confusing verdict. In August 1996, the military court found Mr. Priebke guilty of complicity in the killings but not guilty of “cruelty and premeditation,” and the case was thrown out on the grounds that the statute of limitations had expired.

At the courthouse, the victims’ family members erupted in shouts. Demonstrators blocked Mr. Priebke inside the building. Then-Prime Minister Romano Prodi promptly laid flowers at the site of the massacre in a display of his disapproval of the court’s decision. At the time when indicted Bosnian Serb leaders Radovan Karadzic and Ratko Mladic were avoiding trial for alleged war crimes in the former Yugoslavia, the Italian justice system did not look good.

“Italy had a date with history, and it has blown it,” Shimon Samuels, an official with the Simon Wiesenthal Center, told the Jerusalem Post after the verdict.

Mr. Priebke’s freedom lasted only a few hours. He was rearrested, facing possible extradition to Germany, and taken to the Regina Coeli prison — the same prison from which a number of the men killed at the Ardeatine Caves had been selected.

During his incarceration, Mr. Priebke told an Italian journalist that his opponents had pursued him because he was a symbol — “like the last of the Mohicans” — and that Jews were “playing a dirty game” on him.

Retrial, conviction

After months of legal maneuvering, the Italian Supreme Court denied his extradition to Germany and ordered a retrial, with Hass as his co-defendant.

In July 1997, a military court convicted both men and sentenced Mr. Priebke to 15 years, suspending all but five years. Mr. Priebke’s appeal of that ruling turned out to be a tactical mistake: The conviction was upheld and he was sentenced to lifetime imprisonment. Because of his age, he served his term under house arrest.

Erich Priebke was born near Berlin on July 29, 1913, said the Nazi files that recorded him as party member No. 3,280,478, according to a Washington Post report from the time of his discovery in Argentina.

Mr. Priebke was orphaned at 7, according to Portelli’s book. He went into the hospitality business at 14 and was working at a hotel on the Italian Riviera in 1933, the year that Hitler came to power and that Mr. Priebke joined the Nazi Party.

He moved up the ranks as a translator for the political police, Portelli wrote, and accompanied top Nazi and Fascist leaders — even Hitler and Benito Mussolini — on visits abroad before being transferred to Rome.

Mr. Priebke’s wife, Alice Stoll Priebke, died in 2004. A complete list of survivors could not immediately be confirmed.

Throughout his life, Mr. Priebke maintained that he was ultimately powerless over the events in Rome in March 1944.

“If I could have stopped that horror, I would have,” he told the court. “But I knew, like all of you, that my refusal of that order, my death, and the persecution of my relatives would not have saved those men.”