Finnish officials said on Friday police suspected a Russian citizen of committing war crimes in Ukraine in 2014 and he was expected to face charges before the end of the month.
Vojislav Torden -- a commander of the Russian far-right, neo-Nazi paramilitary Rusich group -- was detained at Helsinki airport in July 2023.
Finland's National Bureau of Investigation (NBI) said it had completed a investigation into several offences dating back to 2014 and suspected Torden of several war crimes, including an "aggravated war crime".
"The suspected crimes took place in autumn 2014 in eastern Ukraine", Detective Superintendent Olli Toyras told AFP.
Toyras, who led the investigation, said he could not reveal further details about the location or nature of the acts.
Finland's supreme court ruled that Torden, formerly known as Yan Petrovsky, could not be extradited to Ukraine due to the risk of him suffering inhumane conditions in prison there.
The investigation, which the NBI launched in December 2023, was carried out in close cooperation with the Ukrainian prosecutor and security services.
Also involved were, Europol, the International Criminal Court and Eurojust -- the European Union Agency for Criminal Justice Cooperation.
Toyras said hearings had been conducted in both Ukraine and Finland.
"The police has closed this case and now the next phase is that the prosecutors will decide if they want to prosecute Torden", Toyras explained.
Prosecutors have until October 31 to bring charges.
Jukka Rappe, Deputy Prosecutor General, told AFP: "Two prosecutors are preparing that indictment. It's possible that a solution can be reached within that timeframe."
Finland has adopted "universal jurisdiction", meaning it can bring charges on its soil for suspected crimes committed anywhere in the world.