Johann Breyer appeared in a Philadelphia courtroom recently to face accusations that he assisted in the murder of thousands of Jews as a guard at the Nazi concentration camp at Auschwitz. He has been charged by German authorities with 158 counts of "aiding and abetting" in murder — one count for each of the 158 trainloads of Jews delivered to Auschwitz in 1944.

Breyer is 89 now. He looked frail and at times seemed confused in court, The New York Times reported. But he told the judge that he understood why German authorities seek to extradite him to stand trial for crimes that happened ... 70 years ago.

Breyer's case rekindles an argument that flared in 2009, when John Demjanjuk, an 88-year-old Cleveland automaker, was deported to Germany to face charges that he had been an infamous Nazi death camp guard named "Ivan the Terrible." (He was convicted but died in 2012, while his case was on appeal.)

Then, as now, some people asked: Is it worth pursuing these cases? Has the statute of limitations run on the Holocaust and the atrocities Nazi war criminals committed?

The answer today is the same as it was in 2009: Genocide carries no statute of limitations. The pursuit of these cases ends when the last Nazi dies.

Breyer says he served as a perimeter guard at the camp, far from the killing. The retired toolmaker came to the United States in 1952. The Justice Department accused him of Nazi ties and tried to deport him in 1992. But that effort failed and the case languished.

Neal Sher, the former director of the Justice Department's Nazi-hunting office, tells us that for years the German government refused to aggressively pursue many similar cases. Nor did the U.S. apply much pressure. Breyer and scores of others "should have been shipped over there a long time ago," he says. "The fact that someone has gotten away with (a war crime) and not paid the price for years doesn't mean he should continue to get away with it."

German authorities reportedly have opened investigations into several dozen suspects now in their 80s or older. We applaud these belated efforts. The hunt must continue.

In 2003, famed Nazi-hunter Simon Wiesenthal announced that he would close his files. He was 94 and he died two years later. "I found the mass murderers I was looking for and I have outlived all of them. If there's a few I didn't look for, they are now too old and fragile to stand trial. My work is done," he said.

But the work to which Wiesenthal dedicated his life — bringing Nazi war criminals to justice — continues. Wiesenthal often was asked why he didn't retire years earlier. He said that his work was about more than stalking former Nazis. It was to stand as a "warning to the murderers of tomorrow."

All over the world, hundreds of former Nazis waited for Wiesenthal to relent. "But as long as we work, they have very bad sleep. And their bad sleep is part of the sentence," he said.

The ranks of former Nazis are dwindling. But authorities around the world pursue the same mission: Make sure none of them sleeps well.

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