The discovery this past week of war criminals in Hungary and Minnesota has given new life to Nazi-hunters who continue despite the advancing age of their prey. In fact, changes in German law may actually lead to the prosecution of more young Nazis who stood guard at death camps during World War II.

“There are at least hundreds if not thousands of them out there,” said Efraim Zuroff, chief Nazi hunter for the Simon Wiesenthal Center. “The question is what are the chances of bringing them to justice.”

Last week, the Associated Press reported that a 94-year-old Michael Karkoc of Minnesota lied to U.S. authorities about his activities during the war, and that he was an SS commander in the Ukraine. The Weisenthal Center has asked the Department of Justice to open an investigation.

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Zuroff has been hunting Nazis for the past 30 years. He relies on tips from the general public about their neighbors or relatives who may be hiding a secret past.

Zuroff noted that an 18 year old at the end of the war in 1945 would now be 86 years old, but people are living longer. He points to Hungary charging 98-year-old Laszlo Csatary with assisting in the deaths of 15,700 Jews while working for the Nazi police in Slovakia.

Csatary fled Europe after the war and worked as an art dealer in Canada before being expelled in 2007. Zuroff got a tip that Csatary was living quietly in Budapest, where he tracked him down in 2011. Csatary was the No. 1 most wanted criminal of the Wiesenthal Center in 2012.

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Zuroff defines a Nazi war criminal as anyone in the service of Nazi Germany or allied with Nazi Germany who participated in prosecution and murder of innocent civilians or those considered enemies of the Third Reich. “No one has any idea how many are still alive today, Zuroff said from his office in Israel. “This is something that took place in every single country in Europe.”

Zuroff said that Austria is likely hiding the largest number of war criminals. There hasn’t been a prosecution there in 30 years, he said.

In Germany, prosecutors recently announced they would begin looking for 50 prison guards for possible war crimes prosecution. German law changed recently to allow documents as well as eyewitnesses as proof of war crimes. As a result, Zuroff foresees a spike in trials in the coming years.

While there were an estimated 10 million members of the Nazi party in Germany during the war, not all of them committed crimes, according to Peter Black, senior historian at the United States Holocaust Memorial Museum in Washington, D.C.

The work of Zuroff and others will likely continue even after the last Nazi is caught.

“The sad fact of human behavior is that even after the last Nazi offender dies,” Black said, “we have more recent generations of participants in mass murder and genocide that are still young enough to prosecute.”