A Polish appeals court has overturned a ruling against two leading Holocaust historians accused of defamation, in a closely watched case that raised questions about the freedom to research Poland’s second world war past. The civil case was brought against Prof Barbara Engelking and Prof Jan Grabowski for a book they co-edited about the complicity of Catholic Poles in the genocide of Jews during Nazi Germany’s occupation of Poland. Night Without End documented several such cases, but the court action was brought by the niece of Edward Malinowski, the wartime mayor of the village of Malinowo in north-east Poland. The book mentions that he may have been implicated in a local massacre of Jews by German soldiers, but his niece, Filomena Leszczyńska, argued he had in fact helped Jews. In February, a lower court ordered Engelking and Grabowski to apologise to Leszczyńska, saying their claim had been “inaccurate”. On Monday, a judge in the Polish court of appeals overturned that ruling, though she did not speak to the accuracy of the book’s passage. Instead, Joanna Wiśniewska-Sadomska said that the litigation constituted “an unacceptable violation of the freedom of scientific research and the freedom of expression”. The “courtroom was not the right place for a historical debate”, the judge added. Verifying research methodology or source material would make for “an unacceptable form of censorship and interference in the freedom of research and scientific work”, Wiśniewska-Sadomska said. The ruling was welcomed by Grabowski and Engelking, who declared it a “great victory” in a Facebook post. “We greet the verdict with great joy and satisfaction all the more, that this decision has a direct impact on all Polish scholars, and especially on historians of the Holocaust,” they said. A Warsaw-based organisation that supported Leszczyńska said it would appeal to the supreme court. The case took place in a tense political climate, with critics accusing the nationalist government of attempting to whitewash Polish history and discourage academic inquiry into cases of collaboration. The Yad Vashem Holocaust memorial and various Jewish organisations and researchers from both sides of the Atlantic condemned the defamation trial. Almost 6 million Poles, including 3 million Jews, perished between 1939 and 1945 during Nazi occupation. The attitudes of Catholic Poles to their Jewish neighbours varied greatly at a time in which even offering a Jewish person a glass of water could be a death sentence. There were many cases of indifference and sometimes cruelty against Jewish Poles that have been documented by historians, but there were also many stories of courage. More Poles – more than 7,000 – have been named “Righteous Among the Nations” than any other nationality, an honour used by Israel to describe non-Jews who risked their lives during the Holocaust to save Jews from extermination. The topic of Polish crimes against Jews was taboo during the communist era and new revelations of Polish wrongdoing in recent years have sparked a backlash. Poland’s ruling Law and Justice party has vowed to fight what it considers unfair depictions of Polish wrongdoing, preferring to promote remembrance of heroism and sacrifice. Many researchers and the Israeli government has accused the Polish government of historical whitewashing.