BERLIN — A German prosecutor on Friday said he has opened a murder investigation against a key witness in the trial of alleged Nazi war criminal John Demjanjuk.

The probe is based on evidence Alex Nagorny may have been involved in mass killings at the Nazis' Treblinka concentration camp in occupied Poland.

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Prosecutor Hans-Joachim Lutz told the AP Friday witnesses say 94-year-old Nagorny took part in the mass shootings of Jewish prisoners in 1941-1942. He is trying to determine if there is enough evidence for charges.

Nagorny has testified in the Demjanjuk case that he served as a guard with Demjanjuk at the Flossenbuerg concentration camp in Bavaria.

He also told the court that he knew nothing of Treblinka, testifying he had heard the name but "why, I don't know."

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