A letter sent to Prime Minister of the Netherlands Mark Rutte said Dutch officials had failed to build a case. They asked that inquiries by the Safety Board and prosecution service be handed over to the UN.

Rutte should “request the UN to appoint a special envoy to take over,” said the letter written by Van der Goen Attorneys.

Malaysia Airlines flight MH17 was downed on July 17 over eastern Ukraine, killing all 298 passengers and crew, two-thirds of them Dutch.

Dutch investigators, leading a case involving 11 countries, have not concluded how the plane was shot down or identified suspects.

The Netherlands “has completely botched” the investigation and the legal framework of the case, said the letter, sent on behalf of 20 relatives from Belgium, Germany, the Netherlands and the US.

Dutch prosecutors have been unable to access the crash site, or not met international requirements to secure evidence, the letter said.