Helsinki District Court on Monday ordered that Voislav Torden, a former Russian mercenary suspected of terrorist crimes in Eastern Ukraine, to be held in custody.
Ukraine has requested that Torden be extradited there, but the Finnish Supreme Court denied the request, declaring that the suspect might be exposed to inhumane conditions in prison there.
The District Court ordered that Torden, 36, be imprisoned on suspicion with probable cause of an aggravated war crime and another war crime in 2014-15.
Finnish prosecutors have until 31 May 2024 to bring charges against him.
The Deputy State Prosecutor decided on Friday to launch a preliminary investigation into Torden alleged crimes.
According to the Supreme Court, there is a real danger that Torden may be placed in a prison in Ukraine where the conditions do not meet the humane treatment requirements of the European Convention on Human Rights.
He founded the neo-Nazi Rusich militant group, which has been accused of atrocities in Ukraine.
The European Court of Human Rights has ruled in several cases that prison conditions in Ukraine violate the human rights convention due to the overcrowding and various deficiencies.
According to reports on the human rights situation in Ukraine, prison conditions in Ukraine have further deteriorated during the war.
There have also been reports of torture and violence against inmates suspected of collaborating with Russia.
Banned from entering Finland
Torden was on an EU sanctions list under his previous name Yan Petrovsky, and was banned from entering Finland.
The ex-commander of the notorious Rusich group was arrested at Helsinki Airport in July on suspicion of terrorist activities. He was caught trying to leave the country using a fake passport.