UNITED NATIONS (Reuters) - Two United Nations sanctions monitors in Democratic Republic of Congo discussed their travel plans with family representatives of a late militia leader the day before they were murdered while investigating the group, according to a confidential report seen by Reuters on Tuesday.

Michael Sharp, an American investigator for the United Nations, found murdered this week in the Democratic Republic of the Congo, is shown in this photo taken in Goma, Congo, February 7, 2017. Courtesy of John E. Sharp/Handout via REUTERS

However, U.N. investigators say they cannot yet lay blame for the murders based on the preliminary evidence.

American Michael Sharp, coordinator of the independent monitoring group, and Swede Zaida Catalan were killed in central Congo on March 12 while carrying out investigations for the annual report to the U.N. Security Council, dated June 30.

The remaining members of the monitoring group wrote that they had retrieved an audio tape, dated March 11, of Sharp and Catalan speaking with representatives of the family of the late Kamuina Nsapu militia leader Jean-Pierre Mpandi, who they said was killed by Congolese troops last August. This is the first time the existence of this tape has been reported.

“Parts of the discussion concerned a field visit scheduled for the following day,” they wrote in the 35-page report. “The tape confirmed that the investigation aimed at a better understanding of Kamuina Nsapu’s structure, its support networks and the potential recruitment and use of children.”

On March 12, Sharp and Catalan left the provincial capital of Kananga to travel toward Bunkonde. At about 4 p.m. they “were executed by a heteroclite group of individuals not yet identified,” wrote the monitors, who said they did not yet have the enough evidence to lay blame for the killings.

“However, the available evidence does not preclude the involvement of different actors, such as (pro or anti-government) Kamuina Nsapu factions, other armed groups, as well as members of state security services,” said the report.

MURKY ALLIANCES

The bodies of Sharp and Catalan were found in a shallow grave two weeks after they disappeared.

More than 3,300 people have been killed and 1.4 million forced to flee their homes in Kasai since the start of the insurrection nearly a year ago by the Kamuina Nsapu militia, which wants the withdrawal of military forces from the area.

Yet the U.N. monitors noted in their report that “throughout 2017 this conflict moved away from an insurrection of a specific community towards a larger upheaval, spreading the Kamuina Nsapu label far beyond its initial confines.”

“Sources told the group that while many factions were hostile to the government, government militias have also emerged operating under the Kamuina Nsapu label,” wrote the monitors, who accused Congolese troops of using “disproportionate violence” against the Kamuina Nsapu.

The Congolese government screened a film to reporters in Kinshasa on April 24, which they said showed members of anti-government Kamuina Nsapu killing the U.N experts.

The video appeared to show Sharp and Catalan walking with a group of men wearing red headbands characteristic of the Kamuina Nsapu militia. The pair are next seen sitting on the ground and then shot. Catalan is subsequently beheaded.

Many analysts say the grainy video of the murders raises more questions than it answers, such as why one of the assassins from the Tshiluba-speaking militia gave orders in Lingala, which is the language of western Congo and the army.

CALL FOR U.N. INVESTIGATION

The same week that Sharp and Catalan disappeared, Kamuina Nsapu representatives met Interior Minister Emmanuel Ramazani Shadary for peace talks in Kananga.

Congolese U.N. Ambassador Ignace Gata Mavita wa Lufuta told the Security Council last week that 11 people had been arrested in connection with the murders, including eight who had been accused of direct involvement.

“The group notes that other key suspects of the murder have not yet been arrested despite available evidence,” the U.N. monitors wrote. “In May 2017 the group spoke to a senior police officer who denounced the lack of cooperation on the side of the government security services involved in the investigations.”

The monitors also warned that the Congolese government’s repeated spreading of the video of the killings “could obstruct ongoing criminal investigations.”

The U.S. Federal Bureau of Investigation, Swedish police authorities and Congolese military justice are conducting criminal investigations, according to the report, and the United Nations has established a board of inquiry into the murders.

The U.N. monitors recommended that the Security Council ask U.N. Secretary-General Antonio Guterres to establish an independent international investigation “to gather evidence, to identify the perpetrators, their support networks and motives.”