DAKAR (Reuters) - An informant for Congo’s intelligence service and an army colonel on Monday denied involvement in the killing of two U.N. sanctions monitors last year, the prosecutor in the case said.

Zaida Catalan, a Swede, and Michael Sharp, an American, were killed in March 2017 while investigating an armed conflict in Democratic Republic of Congo’s Kasai region between government forces and the Kamuina Nsapu militia.

Reuters and Radio France Internationale (RFI) revealed in December that Jose Tshibuabua, who helped Catalan and Sharp plan their fatal trip the day before they left, was working at the time as an informant for Congo’s intelligence agency (ANR).

The report revived questions about what role state agents may have played in the killing of the monitors, who had been investigating a conflict in which Congolese forces have been implicated in atrocities by the United Nations and human rights groups.

Congo’s government has blamed the militia from the start and has arrested two dozen individuals. But it said last December it could not exclude the possibility that state agents were involved.

On Monday, Tshibuabua, who was arrested late last year, and Colonel Jean de Dieu Mambweni, who has not been arrested, appeared before the court that is trying the case.

Tshibuabua told the court in the Kasai city of Kananga that he only learned on the radio three days after the March 12 killings that Sharp and Catalan had gone missing, prosecutor Timothee Mukuntu told Reuters.

Tshibuabua, a cousin named Betu Tshintela, who served as Sharp and Catalan’s translator for their trip, and others linked to Kamuina Nsapu’s ruling family met the experts on March 11 in Kananga to help them organize their mission to the village of Bunkonde the next day.

The bodies of Sharp and Catalan were discovered in a shallow grave two weeks later. Tshintela and three moto taxi drivers who accompanied them on the mission went missing and have not been found.

Security sources have told Reuters and RFI that Colonel Mambweni put Sharp and Catalan in contact with Tshintela. But before the court on Monday, he denied having done so, Mukuntu said.

Phone logs from the prosecutor’s file seen by Reuters and RFI also show that both Tshibuabua and Mambweni exchanged text messages in the days leading up to the killing with the provincial ANR chief, Luc Albert Tanga Sakrine.

Tanga Sakrine has declined to comment on the case. Mukuntu said he did not ask about contacts with Tanga Sakrine but that the issue could come up at a future hearing.