Four members of a family were found dead on Christmas Eve in Liechtenstein.

Police on Wednesday discovered the bodies of two men and two women, suspected to belong to the same Liechtenstein family, authorities in the Alpine principality said.

Local police said the body of a 41-year-old Liechtenstein man was found at around 10:30 a.m. on the Swiss side of the Rhine River near the capital Vaduz. The cause of death remains unclear, Swiss authorities said.

According to Reuters, further investigations led police to an apartment in Vaduz, where the bodies of a 73-year-old man and two women, aged 68 and 45, were discovered.

According to preliminary findings, the three victims were the parents and sister of the 41-year-old man, Liechtenstein police said in a statement. A police spokesman confirmed that the causes of their deaths are still being determined.

The State Police Criminal Investigation Department is investigating the case with the involvement of a large number of officers.