(ABC News) -- Polish prosecutors have pledged to help U.S. investigators bring to justice a 94-year-old man living in Minnesota, who is accused of being a former commander of a Nazi SS unit responsible for killing scores of women and children during World War II.
A lengthy investigation across six countries led the Associated Press to discover Michael Karkoc living quietly in Minneapolis. Karkoc is accused of leading the SS-led Ukrainian Self Defense Legion, an organization whose members massacred civilians and resistance fighters throughout Ukraine and Poland and helped suppress the Warsaw Uprising.
Members of the legion were barred from entering the U.S. after the war. Documents obtained by the AP indicate that when emigrating to the U.S. in 1949, Karkoc lied about his role in the war, telling American officials he spent those years working for his father and then in a labor camp.
Polish officials pledged today to help with any investigation, but said it was too early to begin taking steps towards extradition.
"Polish prosecutors will help American investigators, there's no doubt," said a Polish embassy official. who declined to be identified because he was not authorized to speak. "Help will be provided to take steps to examine the evidence. Based on the evidence a decision on extradition will be made."
Most of the crimes affiliated with Karkoc's group occurred in Poland, including the 1944 directive to "liquidate all the residents" of the village of Chlaniow, according to documents from a Soviet-era investigation, discovered by the AP.
Both Poland and Germany may each ultimately seek to prosecute Karkoc in their own countries.
Under German law, former Nazis with "command responsibility" can be charged with war crimes.
The Department of Justice, which handles such cases in the U.S., would not comment on an open investigation, but has used lies found in immigration papers to deport suspected war criminals in the past.
"While we do not confirm or deny the existence of specific investigations, I can say as a general matter that the Department of Justice continues to pursue all credible allegations of participation in World War II Nazi crimes by U.S. citizens and residents," spokesman Michael Passman told ABC News.com in an email.
Calls made to Karkoc's home were not answered.
Despite keeping his alleged role in the war a secret in the United States, Karkoc published a memoir in Ukraine in 1995, outlining his role in organizing and leading the Ukrainian Self Defense Legion in collaboration with the Nazis.
A British pharmacist who is an amateur historian researching the group came across the book and reached out to the AP for help tracking down Karkoc in the U.S.
Karkoc emigrated to the U.S. in 1949 with two sons after the death of his first wife. He settled in a Ukrainian neighborhood where he worked as a carpenter, remarried and had four more children, according to the AP.
"It doesn't come as a surprise," said Aaron Breitbart, a senior researcher at the Simon Weisenthal Foundation. "It is estimated that between 3,000 and 10,000 people entered the U.S. with dirty wartime pasts, who should not have been allowed in."
Breitbart indicated that Karkoc will likely outlive the judicial process.
The U.S. doesn't try these war criminals, but instead seeks to denaturalize and deport them. In some cases, foreign countries will ask for the suspect to be extradited.
In either case, the process is incredibly lengthy and can take years in court.
"It can take years and years by time courts say he can be deported," said Breitbart. "A good defense lawyer will drag it out until the guy gets biological amnesty. That is, until he dies."
Despite such suspects' advanced age, Breitbart said it remains important for governments to go after them. "People need to know if you participate in a heinous crime, there is always someone looking for you."
Karkoc's case is reminiscent of that of John Demjanjuk, a Ukrainian who emigrated to Ohio after the war. Demjanjuk was accused of collaborating with the Nazis and overseeing the deaths of more than 20,000 Jews at several concentration camps including Sobibor.
After years of accusations, research, and court proceedings, Demjanjuk was finally deported to Germany in 2009. In 2011, the 91-year-old was found guilty of being an accessory to murder and sentenced to five years. He died the following year.