Germany launched a war crimes investigation against Johann "Hans" Breyer after years of failed attempts by the US to revoke his citizenship.
"Old age should not protect people who committed such heinous crimes," Efraim Zuroff said Monday by phone from Israel.
Breyer, who has resolutely denied the allegations against him, told The Associated Press in an interview at his home last week that he was never at the camp.
"I had nothing to do with the camp. I told them over and over," he said, recalling a years-long failed effort by the US to strip him of his citizenship.
Instead, Breyer said he was at a nearby SS camp where he was trained to use a light infantry cannon.
On Sunday, Breyer repeated that he's not been contacted by Germany nor notified that he's under any investigation.
"I heard this from you," he told an AP reporter, reiterating that he was never a guard.
On Monday, a few reporters were parked outside the three-level row home he shares with his wife. No one answered the door but a handwritten sign read: "We do not have any comment. Please leave."
Breyer did not respond to messages left at his home.
Some neighbors declined to comment while others did not answer their doors.
For more than a decade, the Department of Justice waged court battles to try to have Breyer deported. They largely revolved around whether Breyer had lied about his Nazi past in applying for immigration or whether he could have citizenship through his American-born mother.
That legal saga ended in 2003, with a ruling that allowed him to stay in the United States, mainly on the grounds that he had joined the SS as a minor and could therefore not be held legally responsible for participation in it.
Accessory to murder?
The Justice Department noted that it had proved, in court, that Breyer was involved in "Nazi-sponsored acts of persecution while serving as an SS guard" at Buchenwald and Auschwitz during World War II.
"However, findings concerning his mother's birth and the date of his SS enlistment made it legally impossible to deport him from the United States," Rebekah Carmichael, a department spokeswoman, told the AP in an email Monday.
"As a general matter, the Department of Justice has a more than 40-year record of close cooperation with European governments that seek to prosecute cases involving Nazi crimes, including through sharing of evidence and facilitation of extradition and deportation," she said.
German officials have not yet filed charges against Breyer, but he could be charged with accessory to murder, the same legal theory that prosecutors in Munich used to try and convict former Ohio autoworker John Demjanjuk on charges that he served as a death camp guard at Sobibor in occupied Poland.
Ukrainian-born Demjanjuk, who died in a Bavarian nursing home in March while appealing his 2011 conviction, was the first person convicted in Germany solely on the basis of serving as a camp guard, with no evidence of involvement in a specific killing.
Under the new legal theory, anyone who was involved in the operation of a death camp was an accessory to murder.
About 1.5 million people, primarily Jews, were killed at the Auschwitz camp complex between 1940 and 1945.