Detained in Finland since July 2023, the 38-year-old Russian citizen was in particular convicted of having disfigured an injured Ukrainian prisoner, the Helsinki court said in its press release.
The prosecution had accused Voislav Torden of five counts of war crimes that resulted in the deaths of 22 Ukrainian soldiers.
The court dismissed the main count against Torden.
The prosecution had argued that the Rusich forces ambushed a convoy of two vehicles, a truck and a car, carrying Ukrainian soldiers on September 5, 2014.
But the court said the prosecution had not proven that Rusich and Torden were responsible for the ambush.
"It has not been possible to conclude from the evidence... that the Rusich unit or group was specifically responsible for organising and carrying out the ambush and arson attack in all respects," the court said.
However, Torden was found guilty of leading the actions of Rusich's soldiers at the scene following the ambush and of killing one wounded soldier.
He was also found guilty of authorising fighters to mutilate Ivan Issyk by cutting the symbol used by the group -- the kolovrat, or "spoked wheel" -- into his cheek.
The emblem is often used by ultranationalist and neo-Nazi groups in Russia and Eastern Europe. Issyk died as a result of his wounds.
Torden was also found guilty of having taken derogatory photos of a fallen soldier at the scene and posting it to social media.
Finland applies "universal jurisdiction", a legal principle allowing it to bring charges on its soil for suspected serious crimes committed anywhere in the world.
