An investigation by the United Nations states that violence in the Democratic Republic of the Congo last year can mean crimes against humanity.
It is said that at least 500 people were killed, including families who were burned alive in their homes, and a two-year-old boy who was thrown into a septic tank.
Ethnic violence erupted when a community wanted to bury one of their traditional chiefs on the land of another community.
The investigation adds that violence can flare up again at any time.
The investigators say that the violence between 16 and 18 December was "planned and carried out with the support of the usual bosses".
Members of the Batende community attacked Banunu villages, "with extreme violence and speed, which allowed little time to escape."
It adds that the provincial authorities in Yumbi, in the province of Mai-Ndombe in the west of the country, seem to have been denied "in their responsibility to protect the people".
The number of victims is probably much higher than the 535 in the report.
In January, the UN said They suspected that at least 890 people had died.
They sent out an investigation team, which reached only three out of the four villages at the core of the attack.
It is believed that bodies were also thrown into the Congo.
The people sought refuge by crossing the Congo to the neighboring Congo Brazzaville. According to the investigation, around 16,000 inhabitants were displaced.
In the presidential election on 30 December, the vote in Yumbi was postponed because of the violence on 31 March. However, opposition candidate Felix Tshisekedi has already been declared the winner.