"Life in prison is the only approriate measure," said the Dutch presiding judge, when considering the gravity and extent of Alemu's crimes.
In fact, during the trial a total of 321 victims were named in four war crimes charges, which included the murder of 75 political opponents and the arbitrary detention in cruel and inhuman conditions of civilians and fighters who had laid down their arms.
During the trial Alemu accepted political responsibility for the Derg's crimes but told judges he did not personally commit them and denied all the charges.
A Dutch resident for almost 30 years, Alemu was the top administrator of Ethiopia's north-western Gojjam province in the late 70s.
But he actually behaved like a henchman to former dictator Mengistu, conducting a reign of terror, prosecutors said.
Several witnesses spoke of "dark cells", where opponents of the Derg were locked up in close confinement for days and faced constant torture.
Alemu was sentenced to death in absentia for Red Terror crimes in his homeland in 2007
Upon hearing the verdict, families of victims applauded.
For them, justice has finally been served.