KINSHASA, Congo (AP) — A suspect has been arrested in connection with the deaths of an American and a Swedish investigator for the United Nations and their interpreter, but another suspect has escaped, a Congolese military official said Friday.

Maj. Gen. Joseph Ponde Isambwa made the announcement in the capital, Kinshasa.

The bodies of American Michael Sharp, Swedish national Zaida Catalan and interpreter Betu Tshintela were found late last month in a shallow grave in Congo's Central Kasai province.

They had been looking into alleged human rights violations by the Congolese army and local militia groups. Three other local members of their team remain missing.

Their deaths raised an outcry, with Sweden opening a murder investigation and Congo's President Joseph Kabila vowing punishment for those responsible.

It was the first recorded disappearance of international workers in the once-calm Kasai provinces, where at least 400 civilians have been killed since August amid a rebellion loyal to former traditional leader Kamwina Nsapu. The United Nations has said 23 mass graves have been found in the region, and at least 434,000 people have been displaced.

The prosecutor of the International Criminal court has said the killing of the U.N. investigators and other violence in Congo could be crimes under her court's jurisdiction.