Authorities in the Democratic Republic of Congo have arrested two people suspected of involvement in the murder of two UN investigators, but one of the prisoners had since escaped.
The announcement was the first reported sign of progress in investigations into the deaths of American Michael Sharp and Swede Zaida Catalan.
Both were members of a group of experts monitoring UN Security Council sanctions against individuals and armed groups in Congo.
Their bodies were discovered in a shallow grave last month, two weeks after they disappeared in Kasai-Central province.
Their Congolese interpreter and three Congolese motorbike drivers who accompanied them have not yet been found, according to the United Nations.
General Joseph Ponde, the army's top prosecutor, did not say when the suspects were detained, but said the remaining one had been transferred between facilities on April 4 - meaning the operation must have happened more than a week ago.
He referred to the one suspect in custody, Daniel Mbayi Kabasele, as an "insurgent" without going into further details or suggesting a possible motive.
Four police officers responsible for guarding the suspects have been arrested following the escape.
Hundreds have been killed and more than one million displaced since last August in central Congo's Kasai region due to fighting between a local militia and security forces, and the UN has identified at least 23 mass graves.