A libel probe has been filed against former Yale professor Jan Gross GRD ’75 by prosecutors in Warsaw, Poland following an op-ed Gross published claiming that Poles  were responsible for the deaths of more Jews than the Germans during World War II.

Gross, a dual American-Polish citizen, wrote about the current European migrant crisis in an article which first appeared on Project Syndicate, an online op-ed platform, on Oct. 13. In the piece, Gross argued that Poland, along with other Eastern European countries, has favored Christian migrants from Syria over refugees of other religions — demonstrating a type of intolerance and xenophobia that dates back to World War II. In an Oct. 15 article in Time Magazine, a spokesman for Poland’s Foreign Ministry denounced Gross’ statement as “historically untrue, harmful and insulting to Poland.” Still, Gross defends his claim.

“I don’t think [the probe] has any merit because one cannot libel if one tells the truth, and I have written the truth so I am not too worried,” Gross told the News.

Gross estimates that between high tens of thousands and 200,000 Jews were killed by Poles during the war, citing testimonies of Jewish Holocaust survivors, post-war trials and diaries to corroborate these figures. Moreover, the Polish Institute of National Remembrance and the Polish Academy of Sciences have conducted similar research that supports Gross’ claim.

While the validity of Gross’ claims remains disputed, his article evidently casts Poland in a poor light. In his piece, entitled “Eastern Europe’s Crisis of Shame,” Gross writes that Poland’s unwillingness to accept non-Christian migrants demonstrates leaders’ “heartless behavior and callous rhetoric” which has been playing into the people’s “intolerant, illiberal [and] xenophobic” attitudes.

The basis of the Warsaw investigation is Article 133 of the Polish Penal Code which stipulates that, “Whoever insults the Nation or the Republic of Poland in public shall be subject to the penalty of the deprivation of liberty for up to three years,” according to the website of the Museum of the History of Polish Jews. Shortly after Gross’ article was picked up by the German newspaper Die Welt, the Warsaw prosecutor’s office received 125 complaints alleging Gross had committed libel under Article 133.

The swift condemnation is far from surprising — Gross has been unpopular in Poland since the release of his book, “Neighbors: The Destruction of the Jewish Community in Jedwabne, Poland.” The book, which was published in 2001, investigates the massacre of Jews by Polish locals in the summer of 1941. Eleven years after the book’s release, it was adapted into the film, “Aftermath” which was banned in many Polish movie theaters. In 2006, a law explicitly prohibiting accusations of Poles committing Nazi crimes was added to the Polish penal code and nicknamed “Gross’ law” in direct reference to Gross and his anti-Polish writings.

“[Gross] has been very controversial in Poland because of his book,” said The Washington Post columnist Richard Cohen.“[Poles] have always been very sensitive on this topic and they are especially allergic to [Gross] … It was well-known at the time that Jews [in Poland during the war] were in as much danger [of] being killed by Poles as they were by Germans … He was probably right because he is an expert.”

In Gross’ article, he claims that while Poles have proved reluctant to accept migrants, their western neighbor, Germany, has held its arms open to the massive influx of immigrants. According to Gross, Germany’s “murderous history” during World War II as opposed to Poland’s history of “victimization” accounts for this contemporary disparity.

“German historians, German politicians, German journalists and German people have come to terms with this sinful past,” Gross said. “It is a much more complicated history for the rest of Eastern Europe because these countries had been victimized during the war … Poland is portrayed as a victim, which it was, but it also happens that local populations got involved in the persecution of Jews.”

Michael Lambert, an Ethics and Excellence in Journalism legal fellow at The Reporters Committee for Freedom of the Press, said the Polish government’s response to Gross’ article shows the difference in how Poland and the United States approach freedom of expression. Lambert said when he learned of the libel probe he was sure it was from a country other than the United States.

Gross said it remains unclear whether Warsaw’s libel probe will result in a formal indictment against him.

“Right now the prosecutor is investigating whether it meets the standard of the law,” Gross said.

Gross, a history professor, is currently on leave from Princeton University.