German police raided the homes of nine elderly men suspected of serving as SS guards at the Auschwitz death camp and arrested three of them on allegations of being accessories to murder.
The arrests came five months after federal authorities said they would investigate former guards at Auschwitz and other Nazi-era death camps.
Their effort was inspired by the precedent-setting trial of John Demjanjuk, who died in 2012 in a Bavarian nursing home while appealing against his conviction on charges that he served at the Sobibor camp. 
"This is a major step," said Efraim Zuroff, the head Nazi hunter at the Simon Wiesenthal Centre in Jerusalem.
"Given the advanced age of the defendants, every effort should be made to expedite their prosecution."
Ukrainian-born Demjanjuk was the first person convicted in Germany solely on the basis of serving as a camp guard, with no evidence of involvement in any specific killing.
Munich prosecutors successfully argued that anyone who was involved in operating a death camp was an accessory to murder. Demjanjuk maintained he had been mistaken for someone else and never served as a guard.
After the Munich ruling, Germany's special federal prosecutors' office responsible for investigating Nazi war crimes announced in September it was recommending charges against about 30 suspected former Auschwitz guards.
The three men arrested this week, aged 88, 92 and 94, all live in Baden Wuerttemberg in southwest Germany. They were taken to a prison hospital, said Claudia Krauth, a Stuttgart prosecutors' office spokeswoman. Krauth said officials had yet to uncover enough evidence to merit the arrests of three other suspects aged 94, 91 and 90.
She said authorities seized "diverse papers and documents from the Nazi era" from the suspects' homes. She declined to provide details.
Five men made no statements, while the 88-year-old admitted being a guard at Auschwitz, but denied committing any crimes, Krauth said.
Prosecutors in Frankfurt said more documents and photographs were seized during raids on the homes of two men, aged 89 and 92, in the neighbouring state of Hesse. Neither suspect was arrested and neither of them made statements.
In North Rhine-Westphalia, state police said they raided the apartment of a 92-year-old man who admitted being an Auschwitz guard, but denied participating in any crimes. They found no incriminating material.
Zuroff, of the Simon Wiesenthal Centre, said the suspects' advanced age should not prevent their prosecution.
"They don't deserve pity," Zuroff said. "They didn't have mercy with the victims, who were often older than they are now."
Many Nazi-era crimes went unpunished after a federal court ruling in 1969 that proof of individual guilt is required. That precedent changed with the Munich ruling.
The Nazis built six main death camps, all in occupied Poland - Auschwitz, Belzec, Chelmno, Majdanek, Sobibor and Treblinka.
Since handing the Auschwitz cases to state prosecutors, federal authorities say they are focusing on identifying guards from other camps, starting with Majdanek. The results of that investigation are expected in a few months.
Additional reporting by McClatchy-Tribune