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.