MINNEAPOLIS — The son of a 98-year-old Minnesota man sought by Polish authorities in connection with a Nazi massacre reiterated Saturday that his father is innocent and asked that evidence against him be released.

A court in Poland issued an arrest warrant for Michael Karkoc last week, opening the way for Poland to seek his extradition from the United States on war crimes charges. The Associated Press had previously identified Karkoc as an ex-commander in an SS-led unit that burned Polish villages and killed civilians in World War II.

Karkoc’s son, Andriy Karkoc, called on U.S. Sens. Amy Klobuchar and Al Franken to intervene in his father’s case “on legal and humanitarian grounds” and to investigate the source of the evidence against him, which Andriy Karkoc says was fabricated by Russian intelligence.

“The Associated Press and the KGB may provide something they say is proof,” he said. “But what they cannot provide is something that is true. My father was, is, and remains an innocent man.”

AP spokeswoman Lauren Easton said the AP stands by its stories, calling them well-documented and thoroughly reported. A spokesman for Klobuchar says the senator believes the matter should be addressed in the criminal justice system, not the U.S. Senate. Franken was traveling from Minnesota to Washington on Saturday and was unavailable for comment.

Earlier this week, prosecutors from the Institute of National Remembrance in Poland said evidence shows American citizen Michael K. 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.

Judge Dariusz Abramowicz said the regional court in Lublin issued an arrest warrant based on 13 volumes of evidence, including documents from the U.S., Germany and Ukraine and from Poland’s archives. He said the evidence was strong enough to seek arrest.

Andriy Karkoc said his father served honorably with the Ukrainian Self Defense Legion, and the actions of other people in the unit might be at issue, but his father can’t be judged guilty by association.

A prosecutor in Lublin, Jacek Nowakowski, said on Polish TV earlier this week that signatures from Nazi times and an application for a U.S. visa helped identify the man.

Poland’s decision to issue an arrest warrant comes four years after the AP published a story establishing that Michael 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 Karkoc lied to American immigration officials to get into the United States a few years after the war.

A second report uncovered evidence that Karkoc himself ordered his men in 1944 to attack a Polish village in which dozens of civilians were killed, contradicting statements from his family that he was never at the scene.

It wasn’t immediately clear when Poland’s Justice Ministry would write the extradition motion, which would then be handled by the Justice Department.

Andriy Karkoc has said his father suffers from Alzheimer’s disease, but Abramowicz said there was no information to suggest that health conditions could hamper Karkoc from standing trial in Poland.

Germany also began investigating Karkoc after the 2013 story. In 2015, they concluded there was enough evidence to pursue murder charges, but they decided he was unfit to stand trial.