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. Their kidnapping was reported March 13. Sharp had established a home base for several years in Hesston, where his parents currently reside. 

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.

The group was due back to the United States to make reports to the United Nations when they went missing. 

Congo is home to multiple militias competing for stakes in the vast Central African nation's rich mineral resources.

Sharp was working with those militias. First entering the region as a mission worker for Mennonite Central Committee, Sharp helped negotiate the release of child soldiers during a three-year term with MCC. After that term, he joined the United Nations team and worked with the generals of the militias.

A 34-year-old graduate of Eastern Mennonite University, Sharp entered voluntary service after college. His first service was in Germany, assisting with military counseling and support. He finished a graduate degree in International Relations and Peace Studies.

He later went into missions with MCC before joining the U.N. He served as Eastern DR Congo program coordinator for MCC from 2012 to 2015. 

The 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.