German prosecutors said Monday that they opened a formal preliminary investigation of a Minnesota man who commanded a Nazi-led unit during World War II, to determine whether there is enough evidence to bring charges and seek his extradition.

The Associated Press found that 94-year-old Michael Karkoc entered the U.S. in 1949 by lying to American authorities about his role in the SS-led Ukrainian Self Defense Legion, which is accused of torching villages and killing civilians in Poland. Evidence indicates that Karkoc was in the area of the massacres, although no records link him directly to atrocities.

Kurt Schrimm, the head of the special German prosecutors' office responsible for investigating Nazi-era crimes, said prosecutors 'have opened a preliminary investigation procedure to examine the matter (and) seek documentation.' It was unclear how long their examination might take.

Schrimm's office is responsible for determining whether there is enough evidence against alleged Nazi war criminals for state prosecutors to proceed with a full investigation and possible charges. The only charges that can be brought in such cases are murder and accessory to murder, as all other offenses fall under the statute of limitations under German law.

Germany has taken the position that people involved in Nazi crimes must be prosecuted, no matter how old or infirm, as it did in the case of retired Ohio autoworker John Demjanjuk, who died last year at age 91 while appealing his conviction as a guard at the Sobibor death camp.

Poland's National Remembrance Institute, which investigates Nazi and Soviet crimes, has said prosecutors are reviewing files on Karkoc's unit for any evidence that would justify charges and an extradition request.

It says the files were gathered during separate investigations into the killings of civilians in the village of Chlaniow, in southeastern Poland, and into Nazi suppression of the 1944 Warsaw Uprising against German occupation. Documentation found by AP shows that Karkoc's unit was involved in both.

Karkoc's son, Andriy Karkos, has said that his father "was never a Nazi," and pointed to the portion of the AP story that said records don't show Karkoc had a direct hand in war crimes. He has said the family won't comment further until it has obtained its own documents and reviewed witnesses and sources.