WARSAW, Poland — Prosecutors in southern Poland have dropped a case into claims made by Holocaust scholar Jan Tomasz Gross that Poles killed more Jews than Germans during World War II.

Gross’ claim in a 2015 article upset many and a probe was subsequently launched on whether the historian insulted the Polish nation.

Prosecutors in Katowice said Tuesday that the evidence gathered offered no clear guidance.

The case against Gross, now a retired Princeton University professor, raised questions about the commitment by Poland’s ruling right-wing Law and Justice party to freedom of research and scholarship.

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