LUDWIGSBURG, Germany — Before Allied forces liberated Nazi Germany and the survivors of Adolf Hitler’s death camps more than 70 years ago, tens of thousands of Nazi criminals who were directly involved in the Holocaust disappeared.

This 1957 photo provided by the US Department of Justice shows Jakiw Palij, a former Nazi concentration camp guard who has been living in the Queens borough of New York. The White House says that Palij, a 95-year-old former Nazi concentration camp guard has been deported to Germany, 14 years after a judge ordered his expulsion. In a statement, the White House said the deportation of Palij, who lived in New York City, was carried out early Tuesday Aug. 21, 2018. US Department of Justice via AP

Some escaped abroad. Others hid in German cities, moving into houses with people they would have sent to their deaths under the Hitler regime.

Few of them faced justice — until now, perhaps.

At least 23 alleged Nazi criminals who are believed to have worked in death camps were already facing charges in Germany and Austria by June, marking a dramatic increase compared with previous decades, according to a document German prosecutors shared with The Washington Post.

On Tuesday, that number increased further, as the White House announced that it had deported 95-year-old Jakiw Palij, an alleged former Nazi guard. The resident of the Queens borough of New York was arrested Monday and deported to Germany early Tuesday, according to the U.S. Embassy in Berlin. Palij was moved to a nursing home upon arrival in the city of Düsseldorf, Germany’s Frankfurter Allgemeine Zeitung newspaper reported.

In a statement Tuesday, U.S. officials indicated that the deportation was the result of “extensive negotiations” and “collaborative efforts with a key European ally,” Germany.

Palij was born in what today constitutes Ukraine but was part of Poland at the time. After the end of WWII, he left Europe for the United States, where he became a citizen in 1957 by hiding his Nazi past. But 17 years ago, in 2001, Palij admitted his involvement with the Nazi SS, Hitler’s feared paramilitary organization. Prosecutors argue that documents prove Palij’s knowledge and participation in the Holocaust, in which more than 6 million Jews and millions of other victims were killed.

Palij admitted to U.S. officials in 2001 that he was trained at the SS paramilitary camp in the town of Trawniki where units were specifically prepared to participate in the Holocaust.

Authorities took away Palij’s U.S. citizenship in 2003, and the former Nazi guard lost an appeals process two years later, but administrative challenges dragged on until now because it was unclear to which country Palij should be deported.

In Germany, Palij will be one of two dozen Nazi suspects whose cases are now under investigation by the country’s dedicated Nazi crimes agency, based in the city of Ludwigsburg, or have already been transferred to local prosecutors.

All the agency’s suspects are in their 90s, and some are likely to die ahead of any sentencing or could be declared unfit to stand trial. More than 70 years on, there is little time to be lost: It could be the last chance for Nazi criminals to face justice for crimes that continue to represent the worst of mankind.

How many more individuals will be charged largely depends on Jens Rommel, Germany’s sixth chief prosecutor for Nazi crimes. “All of my five predecessors assumed that they’d be the last person in this office,” said Jens Rommel.

“In recent years, though, we’ve made some remarkable progress,” said Rommel.

It’s a remarkable turnaround, given that there was little reason for such enthusiasm only a few years ago, after German prosecutors for decades faced hurdles that made it impossible to charge a wide range of suspects despite evidence of their Nazi past.

“By 1960, murder and abetting murder were the only Nazi-era crimes that prosecutors could charge,” Elizabeth Barry White, a senior historian with the Holocaust Memorial Museum in Washington, explained last year. High-ranking Nazi officers were often only charged with lesser offenses because their direct responsibility for the killing of one or more individuals could not be proved based on the narrow German jurisdiction. In many cases, lower-ranking guards or soldiers such as Palij were not even prosecuted at all.

“As time passed and the higher-ranking perpetrators died out, the pool of potential defendants shrank to those against whom evidence was hardest to find,” White said. A new approach was needed, and it came after a court convicted former Nazi guard John Demjanjuk in 2011.

Before 2011, prosecutors needed to provide evidence that guards had themselves murdered Jews or other Nazi opponents. But the Demjanjuk verdict was based on a dramatically different approach: His mere presence at the Nazi death camp was sufficient to establish responsibility for the killing.

This 1942 photo provided by the the public prosecutor’s office in Hamburg via the United States Holocaust Memorial Museum, shows Heinrich Himmler, center left, shaking hands with new guard recruits at the Trawniki concentration camp in Nazi occupied Poland. Trawniki is the same camp, where some time after this photo was made, Jakiw Palij trained and served as a guard. Public prosecutor's office in Hamburg via the United States Holocaust Memorial Museum via AP

Demjanjuk later appealed the sentence but died before a court could evaluate his claims. The new legal framework’s viability was only proven two years ago when another former guard lost his appeal following a similar sentence.

At the time, many feared that it may also have been the last.

And while the verdict may have led to the sentencing of hundreds more guards if it had come years earlier, the recent increase in investigations has led to new optimism among Germany’s Nazi prosecutors, said chief prosecutor Rommel, sitting in his Ludwigsburg office filled with books about the Nuremberg trials and a map of WWII Germany.

Rommel and his colleagues mainly rely on documents found in archives or in memorial sites of former death camps. The unit’s eight investigators then painstakingly compare the entries found in equipment or sick lists to establish a suspect’s identity. Once they’ve found a possible match, Rommel’s team checks whether the individual could still be alive.

“In 95 percent of cases, this isn’t be the case,” Rommel said.

In the agency’s basement, tens of thousands of paper documents are stored that include details on convicts or clues that may eventually give away the identities of more suspects. It’s the world’s most comprehensive database of Nazi criminals.

But as German authorities assumed that active cases were going to drop, the archives were never digitalized. The agency’s bureaucratic paper trail isn’t the only challenge. Cases are also slowed because the Ludwigsburg-based Nazi crimes agency handles only early stage investigations that are later taken over by local prosecutors. “It takes time for prosecutors to review and understand the evidence [and] given the age of the suspects, their capacity to stand trial can change very quickly, so that a once-promising case can overnight become impossible to prosecute,” explained historian White.

Investigators aren’t sure how long they will be able to continue their work, because of the advanced age of the identified suspects.

Walking through his agency’s headquarters, surrounded by thousands of files cards with details on the Nazi criminals he and his predecessors hunted, Rommel acknowledged that the job had taken a personal toll on the investigators, especially as time is now running out.

“I don’t take those papers home with me. I just wouldn’t be able to let it go,” he said.