The man lived under a false identity in Finland when he was arrested at Helsinki airport last year, on his way to Nice in France for a family vacation.
The war crimes he is charged with were committed in the Russian-backed separatist region of Luhansk in Ukraine in September 2014. According to the Finnish newspaper Hufvudstadsbladet, he, as the deputy commander of the Russian paramilitary force Rusich, lured two vehicles with a total of 26 Ukrainian soldiers into a trap.
21 of the soldiers were killed on the spot, and another died later from their injuries. The remaining four were seriously injured.
According to the prosecutor, the man, now 37, has violated the Geneva Convention and other international agreements on the laws of war. He is also said to have fought for Russia in Syria.
The Supreme Court in Finland has previously ruled that the man cannot be extradited to Ukraine, due to the risk of his human rights being violated in a Ukrainian prison.
The trial will continue until the end of January, and the prosecutors are demanding life imprisonment. According to the man's lawyer, he denies all five charges.
The Russian paramilitary ultra-right group Rusich was formed in connection with the Russian occupation of Crimea and eastern Ukraine in 2014.
The group is notorious for its brutality and neo-Nazi ideology and is listed as a terrorist organization in Ukraine.
Several members are suspected of committing numerous serious war crimes. The men are said to have, among other things, cut off the ears of prisoners of war, branded victims with swastikas, and raped women in front of their children.
According to several reports, Rusich is financed by the Russian state and has had close ties to the paramilitary Wagner group.
Sources: HBL, Royal United Services Institute (Rusi), Radio Free Europe/Radio Liberty
