Polish investigators working with a British Holocaust researcher say they have confirmed the identity of a man living in Minnesota as the same man wanted for questioning about war crimes against Jews and others.

Associated Press reported that an arrest and extradition request is to be filed for Michael Karkoć, who born in western Ukraine and who has already said he was in the Waffen-SS. Extensive research by Polish publication Kresy.pl helped track him down, on the suggestion that he may have led a unit responsible for an infamous massacre.

Officials at the Polish Institute of National Memory (IPN) have long said that Karkoć commanded the Ukrainian Self-Defence League, which is reported to have massacred civilians in the villages of Korchunok and Chłaniów, the latter in response to the killing of a German commander.

Karkoć, who has lived peacefully in Minneapolis for decades, is believed to have gained a U.S. visa by not disclosing his past. He was identified with the help of Stephen Ankier, a retired British pharmacologist, using photographic analysis.