Two suspected far-right extremists went on trial over the killing of regional politician Walter Luebcke at Higher Regional Court in Frankfurt on Tuesday.
Luebcke's wife and two sons were also present at the hearing as co-plaintiffs.
The family spokesperson Dirk Metz said it was not an easy decision and that the family «wants to send a clear signal against hatred and violence.»
«The family wants to show that it doesn't matter on the internet or in the real-life one cannot fall silent in the face of such violence,» said Metz.
The family lawyer Holger Matt said: «We are willing to use all possible means that we have as joint plaintiffs to make our contribution to solve this crime and cooperate in the conviction of the defendants.»
The hearing was held with tight security measures and limited media and visitors access which led to queues outside the building.
65-year-old head of the regional government in Kassel, Walter Luebcke, who was known for defending chancellor Angela Merkel's welcoming policy towards refugees, was shot dead on June 2, 2019.
The main defendant Stephan Ernst first confessed the crime but later retracted his testimony. Another suspect — Markus H. — allegedly assisted the crime by training Ernst.