Prosecutors said Dadayev, a former soldier in Chechnya's notorious Sever battalion, fired the fatal shots, and Anzor Gubashev drove the getaway vehicle.
Ilya Yashin, a fellow opposition activist, praised the jury for bringing a "just verdict against the bandits who denied..." Four other men were found guilty of involvement in the killing.
But they still insist the evidence clearly shows that those close to Kremlin-loyal Chechen strongman Ramzan Kadyrov - or Kadyrov himself - were actually behind the assassination.
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All five defendants pleaded not guilty, a position they reaffirmed in their closing statements on June 21. He claimed that the slaying was organized by a former Chechen separatist who fought against pro-Russian forces in eastern Ukraine.
Prosecutors said the men committed the crime because they were promised 15 million rubles ($254,000).
On Feb. 28, 2015, the defendants spent some 10 hours in a vehicle parked outside Nemtsov's apartment in central Moscow. As the two walked to cross the Moskva river, Dadayev shot Nemtsov in the back six times, killing the 55-year-old politician on the spot, investigators said.
Lawyers for his family said they were convinced that all of the accused, with the exception of Bakhayev, were involved. The court also ignored their requests to summon Kadyrov as a witness. One of the accomplices was killed during a police attempt to arrest him.