On January 30, 2015 Grand Duke of Luxembourg Henri and the Prime Minister, Minister of State, Xavier Bettel, participated in the commemorative ceremonies to mark the 70 anniversary of the murder of prisoners of the German prison Sonnenburg (currently in Slonsk, Republic of Poland).

They honored the victims of the massacre of Sonnenburg, which took place at the end of World War II and was the largest mass crime ever perpetrated against citizens of Luxembourg. Indeed, on the night of 30 to 31 January 1945, 819 prisoners, including 91 young Luxembourgers, were massacred by SS forces in the Sonnenburg prison.