American authorities have asked three medical experts to determine whether a 99-year-old Minnesota man can travel to Poland to face trial on charges that he was involved in Nazi war crimes during World War II.

Ukrainian-born Michael Karkoc, who lives in Minneapolis, was identified by The Associated Press in 2013 as a former commander of an SS-led Nazi unit that burned Polish villages and killed civilians during the war.

Poland asked the U.S. to hand over Karkoc for trial last July. It was not immediately clear when Karkoc would be examined to determine his fitness to traval.

Karkoc's family denies that he was involved in any war crimes. On Thursday, his son, Andriy Karkoc, issued a statement saying: "My father was, is and remains innocent. We look forward to his complete exoneration."

Prosecutors from Poland's National Remembrance Institute claim that evidence shows that American Michael K. — whose last name they haven't released in line with Poland's privacy laws — was a commander of a unit in the SS-led Ukrainian Self Defense Legion that raided eastern Poland's village of Chlaniow in July 1944, killing 44 people, including women and children.

The investigation was opened after The AP published a series of stories establishing that Karkoc commanded the unit, based on wartime documents, testimony from other members of the unit and Karkoc's own Ukrainian-language memoir. The AP also established that Karkoc lied to American immigration officials to get into the United States several years after the war.

German prosecutors also opened an investigation into Karkoc after The AP's 2013 stories. In 2015, they concluded there was enough evidence to pursue murder charges, but shelved their investigation, deciding Karkoc was unfit to stand trial based upon medical reports from his own doctors.

Andriy Karkoc reiterated that Thursday, saying his family provided copies of his father's physical and mental health records to the German government in 2015, and the Germans suspended their investigation based on those records. He said the records were also provided to the director of the U.S. Department of Justice Human Rights and Special Prosecutions Section.

Karkoc said as of Thursday, the family hasn't heard from anyone at the Polish Embassy, the State Department or the Department of Justice.

State and Justice both said it's their policy not to comment on specific extradition requests.

The Associated Press contributed to this report.