An off-duty police officer fatally shot Andrei Karlov at a photo exhibition in Ankara on Dec. 19, 2016. The officer was later shot dead at the scene by police, AP reported.
Turkish prosecutors say Gulen's network was behind the killing, which they say aimed to derail warming ties between Turkey and Russia. Nine people were arrested. Others, including Gulen, are on trial in absentia on Tuesday.
Prosecutors are seeking life prison sentences for some of the defendants and maximum 15-year terms for others.
Gulen has denied involvement in the coup and in Karlov's killing.
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