He wrote that Poles, not German occupiers, committed the atrocity, thus revising a major part of Polish self-understanding of their history during the war.

[10] A subsequent investigation by the Polish Institute of National Remembrance (IPN) supported some of Gross's conclusions but not his estimate of the number of people murdered.

"[13] Gross's latest book, Golden Harvest (2011), co-written with his wife, Irena Grudzińska-Gross, is about Poles enriching themselves at the expense of Jews murdered in the Holocaust.

"[14] On 6 September 1996, President Aleksander Kwaśniewski awarded Gross and his wife Irena Grudzińska-Gross the Order of Merit of the Republic of Poland[16][17] for "outstanding achievement in scholarship".

[19] Also in 1982, as an assistant professor of sociology at Yale University, he received a Rockefeller Humanities Fellowship for his project "Soviet Rule in Poland, 1939-1941".

"[22] According to historian Jacek Leociak, "the claim that Poles killed more Jews than Germans could be really right—and this is shocking news for the traditional thinking about Polish heroism during the war.

"[23] Polish Foreign Ministry spokesman Marcin Wojciechowski dismissed Gross's statement as "historically untrue, harmful and insulting to Poland".

Prosecutors had previously examined Gross's books Fear and Golden Harvest but closed those cases after finding no evidence of a crime.

[24][22] In 2016, the Simon Wiesenthal Center said the decision to continue the investigation bore "all the hallmarks of a political witch-hunt" and was a "form of alienating minorities and people who were victimized".

Prosecutors said that "there is no conclusive data on the numbers of Germans and Jews killed as a result of actions committed by Poles during the Second World War.

One of the experts consulted was Piotr Gontarczyk, who said there is no conclusive evidence that Poles killed more Jews than Germans during the war, but such a view is impossible to disprove.