Russell Bentley, an American pro-Kremlin fighter, was killed under previously unclear circumstances.

Bentley, a 64-year-old from Dallas, Texas, joined pro-Russian separatists in 2014 to combat Ukrainian forces.

Bentley went missing in the Russian-occupied city of Donetsk in April and was later found dead.

Russia’s Investigative Committee announced that Bentley was tortured to death by Russian soldiers.

The suspects identified by Russia’s Investigative Committee are Russian Armed Forces servicemen Vitaly Vansyatsky, Vladislav Agaltsev, Vladimir Bazhin, and Andrei Iordanov.