Prosecutors believe the suspect who now lives in Finland, committed crimes against humanity in Sierra Leone and Liberia.
A Finnish court of appeal has begun hearing an international war crime case in which a Sierra Leonean man is charged with murders, rapes and other atrocities during the Liberian civil war between 1999 and 2003.
The session began on Tuesday.
Prosecutors argued the 53-year-old suspect Gibril Massaquoi – who has denied any wrongdoing – murdered, raped and mutilated civilians as a top official of the Revolutionary United Front.
The RUF was a militia that fought in Sierra Leone, but also in Liberia for its ex-president Charles Taylor.
Last year, Massaquoi, who has lived in Finland for many years, was acquitted of all charges by a lower Finnish court. It said a significant doubt remained about his participation in the suspected acts due to witnesses changing their testimonies.
But the prosecutors took the case to the court of appeal in Turku, whose members will travel to Liberia and Sierra Leone to hear witnesses again in the coming months, the court said.
Liberia endured conflicts that killed approximately 250,000 people between 1989 and 2003, when Taylor, who seized power in a coup that sparked the rebellion, stepped down.
Thousands of people were mutilated and raped in fighting that involved drugged fighters and child soldiers conscripted by strongmen.
Taylor was convicted and sentenced to 50 years in prison for war crimes by a United Nations-backed Special Court for Sierra Leone in The Hague in 2013.
In November, a French court sentenced former Liberian rebel commander Kunti Kamara to life in prison for atrocities committed during the first Liberian civil war.
Massaquoi’s case is the second international war crime case Finland is dealing with, after a former Rwandan pastor, Francois Bazaramba, was sentenced to life in prison in 2012 for participating in genocide in his native country in 1994.
The Turku court expects to conclude the case in June, it said.