New York - A United Nations board of inquiry said two UN experts were likely murdered in March by militia members from Democratic Republic of Congo's violence-torn Kasai region, but it said further investigations and judicial proceedings are needed to determine the identity and motive of the killers.The board's executive summary, which was obtained on Wednesday by The Associated Press, said that "there was a reasonable likelihood that the killings were committed after consultation with other local tribal actors."Michael Sharp of the United States and Zaida Catalan, a dual national of Sweden and Chile, disappeared on March 12 and their bodies were discovered in shallow graves on March 27.The board's report, sent to the UN Security Council by Secretary-General Antonio Guterres, said there is "a reasonable likelihood" the same militia members were responsible for the deaths of a Congolese interpreter and three motorcycle drivers accompanying the two experts. Their bodies have not been found.The five-page summary noted that information is circulating about the possible involvement "of various government individuals or organisations" in the killings. "This does not provide proof of intent or motive" by anyone - or preclude "that others are involved," the board said.The board said additional investigations, including by national authorities, "may provide greater clarity on this issue."Guterres said in a letter to the Security Council transmitting the board's summary that he intends to discuss "the establishment of a follow-on mechanism and its mandate" with Congolese official and council membersIda Sawyer, Central Africa director at Human Rights Watch, said late on Wednesday the secretary-general needed to take responsibility for uncovering the truth of the two UN experts' deaths following the board's inconclusive results."Since Congolese security forces may have been responsible for the killings, the Congolese government cannot be relied on to find the killers," Sawyer said."Guterres should set up a UN investigation to uncover the truth and help US and Swedish authorities as they work to build cases against those responsible for this heinous crime," she said.Sharp and Catalan were part of an expert group monitoring sanctions against DRC and had gone to Kasai to gather information on armed groups, the sources of violence, and reports of the purposed use of children as fighters, the board said.It said they "were assassinated in a premeditated set-up" under circumstances that are still unclear.The panel said its members retrieved an audiotape dated March 11 in which Sharp and Catalan discussed a field visit the following day with representatives of "the Kamwina Nsapu family," a militia active in Kasai whose customary chief Jean-Pierre Mponde was killed by Congolese soldiers in August 2016.The panel, whose report is scheduled to be discussed by the Security Council on Thursday, said, "The tape confirmed that the investigation aimed at better understanding Kamwina Nsapu's structure, its support networks and the potential recruitment and use of children."Its report said that on March 12, Sharp, the panel's coordinator and expert on armed groups, and Catalan, a humanitarian expert, embarked on a field visit from Kananga, the provincial capital of Kasai Central, toward the locality of Bunkonde.Before arriving in Bunkonde, sources reported that a militia group gathered near the Moyo River crossing close to the village of Moyo Musuila and fired a shotgun to stop the motorbikes the experts were traveling on, wounding one of the drivers, the report said.The board said Sharp and Catalan were accosted "by persons who appeared to be members of a local militia group" who killed them near the village of Moyo Musuila, about 10-15 kilometers from Bunkonde."These facts were established based on a video recording of the incident by a member of the militia group," the board said.It said that based on information from witnesses, 10 individuals from the video have been identified but there is a lack of additional physical or forensic evidence.The board said Congolese authorities have arrested two men who appeared on the video and 10 men who didn't appear "but who are believed to be members of the militia group involved." The board said it was informed that proceedings against the suspects were being conducted in a military court.