For years, Michelle and John Sharp had collected mementos of the peripatetic life of their son Michael and hung them on their kitchen wall, including a map of Africa, a photograph of his visit to the United Nations, and a picture from his hundred-mile hike along the shores of Lake Kivu in the Democratic Republic of the Congo. Michael Sharp, an expert on armed groups, had lived in Africa for years and worked for the U.N. To his parents, he was doing his part to make the world a better place. Their kitchen wall in Hesston, Kansas, served as a kind of homage to his missions.

But the wall has become more akin to a shrine since Sharp and his Swedish colleague Zaida Catalán were brutally killed in a remote village in the central Congolese province of Kasai on March 12, 2017. The map now highlights the area where the two were investigating atrocities against Congolese civilians in the final weeks of their life. A small dot denotes the regional capital, Kananga, where Sharp and Catalán spent their last night. Though nearly 20 months have passed since the killings, many of the details remain unclear to the Sharps, and not a single person has been brought to justice. Three Congolese drivers and an interpreter who accompanied Sharp and Catalán on their last trip are still missing.

A U.N. panel that examined the murders—the first ever of U.N. experts in the course of their work—concluded last year that Sharp and Catalán most likely drove into an ambush ordered by a local tribal chief. John Sharp said the U.S. official who chaired the panel, Gregory Starr, told him that his son and Catalán flouted U.N. security protocols designed to ensure their safety. “He said they operated like cowboys,” John Sharp said in an interview. “Irresponsible is what he meant, they were being irresponsible.”

But a joint investigation by Foreign Policy, Radio France Internationale, Le Monde, Sveriges Television, and Süddeutsche Zeitung reveals that the U.N. buried evidence suggesting that Congolese authorities may have been involved in the murder. FP and the other news organizations reviewed thousands of pages of internal U.N. documents and interviewed dozens of key players for the investigation. It’s not clear from the documents why the Congolese authorities would have wanted Sharp and Catalán dead. But one possibility is that they sought to prevent the investigators from uncovering evidence of government atrocities in the Kasai province.

The Sharps believe the U.N. panel led by Starr withheld critical evidence in order to avoid a diplomatic rupture with the Democratic Republic of the Congo. They and Catalán’s family have tried to persuade the U.N. and the world’s major powers, including the United States, China, and Russia, to create an independent international investigation to pursue the killers. But they have been rebuffed on the grounds that the Congolese government—the likely culprit in the case—bears primary responsibility for investigating crimes on Congolese soil.

“My question all along was, why would anyone target them?” Michelle Sharp told FP. “The only people who would have wanted to shut them down had to be the government because of what they would find out.”

The Kasai province has been wracked by violence since August 2016, when government forces killed the leader of the powerful Kamuina Nsapu militia. Clashes that ensued between the Congolese military and armed groups in the province killed at least 5,000 people and prompted the exodus of more than 1.4 million others.

Human rights groups believe Joseph Kabila, who has been president of Congo since 2001, has been stoking the violence in Kasai in order to justify delaying upcoming elections. They say government forces deployed in the region are arming and equipping local militia and killing civilians. Last year, U.N. investigators documented dozens of mass graves in Kasai.

It was against this backdrop that Sharp, 34, and Catalán, 36, boarded a U.N. plane from Goma, in eastern Congo, to Kananga, a major city in the Kasai region, on March 8, 2017. They planned to collect information on armed groups in the region and the recruitment of child soldiers, as well as investigate reports of large-scale killings.

The U.N. experts had already conducted a reconnaissance visit to the region two months earlier. This time, they planned to interview militia leaders and civilians. They hired Betu Tshintela, a local interpreter, and three motorcycle drivers to take them to the town of Bunkonde.

“We’ll be down south today to meet some of the groups,” Sharp texted a journalist friend, Sonia Rolley. “Should be back before late to catch up.”

On that first day of their trip, somewhere near the village of Moyo Musuila, armed men fired on their convoy, hitting one the Congolese drivers. About a dozen of the armed men apparently took Sharp and Catalán from their motorcycles and marched them through a desolate field.

What happened next was video recorded on a camera phone belonging to one of the killers.

“Speak to them gently, or they may try to run away. Don’t stress them out,” one of the men is heard saying off camera in the regional language Tshiluba. Sharp and Catalán are led through the brush and instructed to sit down beside a tree, facing one another. “Right here, we execute them without them realizing it.”

The video, which was viewed by FP, shows Sharp being shot in the head with a 12-gauge shotgun. Catalán makes a final plea for mercy and then tries to flee but is shot in the back.

Three more shots are heard and then one of the assailants is seen cutting a lock of Catalán’s hair. The group’s leader, who is delivering orders off camera, instructs the killers to decapitate her. “Save your bullets,” he says. “Don’t waste them. They are already dead. Let’s cut the head and get going.”

The faces of at least some of the perpetrators are easy to identify in the footage. They are dressed in the customary red headbands and bandanas associated with the local Kamuina Nsapu militia. A one point, one of the killers proclaims: “In the name of the great chief, we are the children of Kamuina Nsapu. If you have come to harm us, you will die.” Those details would lead the U.N. investigative panel, known as the Board of Inquiry, to conclude that Sharp and Catalán had stumbled into a hostile local militia.

But others who viewed the video spotted inconsistencies. “There was something a little bit wrong,” recalled Rolley, a French journalist and friend of Catalán and Sharp who arranged to have the audio translated.

For one thing, the man delivering the orders spoke occasionally in Lingala, a language commonly used by members of the Congolese military. That fact and others led some of the U.N. investigators, working separately from the Board of Inquiry, to suspect that the killing may have been a premeditated government hit.

“There is a risk that premature conclusions, based on video of the murder of Sharp and Catalán, could be drawn,” one senior U.N. official wrote in a memo to the U.N. Board of Inquiry. “The truth of the matter is likely to be far more complicated than the appearance of a militia-based operation.”

That assessment is borne out by some of the documents related to the investigation. Phone logs viewed by FP show that the main suspects in the killing were in regular contact with Congolese military authorities. Other documents suggest that Congolese military officers routinely interfered with the U.N. investigation into the killings.

Around the time of the killing, Catalán’s sister, Elizabeth Morseby, received a call from Catalán’s cell phone. She was preparing dinner in her mother’s kitchen on the Swedish island of Oland, she said in an interview earlier this month. Morseby could hear deep breathing and the voices of several men speaking in a foreign language.

“I thought initially that maybe they were at a cafe,” she said. “I tried to say hello, Zaida, hello, talk to me, are you there? And Zaida didn’t respond.”

She and Catalán’s mother, Maria Morseby, tried to call Catalán back several times but got no answer. Maria Morseby had spoken to her daughter the night before and could sense her anxiety. She tried Sharp on his cell phone but also got no answer. She quickly typed up an email to U.N. headquarters in New York: “I am deeply concerned that something might have happened to my daughter.”

Jeffrey Feltman, a former top State Department official who was serving as U.N. undersecretary-general for political affairs—which managed the expert panels—was one of the first people to be alerted that Sharp and Catalán had gone missing.

In an interview with FP, he recalled feeling the same sense of dread he felt when reports reached the State Department five years earlier indicating that his close friend, Chris Stevens, the U.S. ambassador to Libya, was trapped in a burning building in Benghazi.

“It was as if time stood still, as though we were in suspended animation,” he said.

As the days passed with no word from Sharp and Catalán, their colleagues gathered in the eastern Congolese city of Goma and began pressing their own sources for leads.

In Kinshasa, David Gressly, the deputy U.N. special representative in the Democratic Republic of the Congo, and Gen. Awale Abdounasir, the U.N. police chief there, quickly set up a task force made up of U.N. police, analysts, and intelligence officials. Their initial effort involved trying to track the phones and other digital devices Sharp and Catalán were carrying.

A battalion of Uruguayan peacekeepers and a team of Tanzanian special forces, meanwhile, launched their own search and rescue operation, hampered by poor weather, dense forest, attacks by local militias, and government obstructions. Fifteen days after the killing, on March 27, the Uruguayans discovered two bodies in a pair of shallow graves on the outskirts of the village of Moyo Musuila. They were quickly identified as Sharp and Catalán.

On Oland, Swedish police knocked on the door of Maria Morseby to deliver the news that her daughter had died. “It was just like life ended. It was the worst day of my life,” Morseby recalled in an interview.

Sharp and Catalán were part of a community of quasi-independent U.N. experts who travel the world to investigate potential sanctions violations from Congo to North Korea. The experts are generally recruited from the ranks of international journalists, scholars, arms experts, and human rights advocates.

For Catalán, a job that required investigative skills and humanitarian instincts was a good fit. Catalán’s father was a Chilean dissident who gained political asylum in Sweden. Her mother was an environmental activist. On her sixth birthday, she approached her mother and asked what she could do make the world a better place, Maria Morseby recalled.

Catalán studied law and worked as an attorney for the Green Party in the Swedish parliament. She also worked in women’s shelters before going abroad to promote women’s rights in Congo, the Palestinian territories, and Afghanistan—where she survived a suicide bombing.

Long before she joined the U.N. panel of experts in 2016, she got a tattoo on her wrist with the Latin phrase “per aspera ad astra,” or “through hardship to the stars.” It served as a reminder of “importance of staying true to one’s purpose and to fight for what is good, in other words always aiming for the stars,” her sister, Elizabeth Morseby, wrote in a text message to FP. After her death, the tattoo helped U.N. peacekeepers identify her remains.

In a coincidence, the tattooed phrase also serves as the motto for the U.S. state of Kansas, where the Sharps live.

Michael Sharp’s path to Central Africa began during his university years, when he studied conflict resolution at Eastern Mennonite University. In 2012, Sharp traveled to eastern Congo as a young missionary, prodding local militias to lay down their arms and return child soldiers to their homes.

His work there caught the attention of the United Nations, which hired him in 2015 as a specialist on armed groups to serve on a panel of experts monitoring enforcement of U.N. sanctions in Congo. He would later be promoted to chair of the Congo panel.

Since Sharp’s death, the family has sought to use the tragedy to draw attention to the suffering of the Congolese people.

“He said, ‘If something happened to me in Congo it would be so ironic, because then maybe the United States and the world would pay attention,’” John Sharp recalled his son telling him. “‘All these years, nobody cares about what is going on in Congo. But if a white guy like me gets killed or something happens,’ he said, ‘the people would pay attention.’ It’s exactly what happened. Exactly.”

On April 24, 2017, more than a month after the killings, the United Nations security chief formed a board of inquiry to establish what had happened, identify the attackers to the extent that was possible, review security procedures, and recommend steps to avoid similar incidents in the future.

The inquiry was headed by Starr, a former U.S. State Department security chief who had previously served as U.N. undersecretary-general in the Department of Security. In that job, Star was responsible for the safety of tens of thousands of U.N. employees around the world.

In a phone briefing with the Sharps, Starr suggested that their son and Catalán may have been victims of a robbery or a black magic ritual. The local militia had been known to ritually kill victims and decapitate them, particularly women and children, to ward off death.

“I see a very mystical, animated tribal group with great suspicions,” he said in the conversation, a recording of which the Sharps shared with FP. The gruesome murder, Starr added, “plays into their very ritualistic magic, when you take people’s body parts that you have slain and you get their power.”

“This is kind of a stretch,” he conceded, “but these people really do believe this stuff.”

But U.N. investigators and journalists had increasingly come to suspect that Sharp and Catalán may have been lured into a trap by Congolese agents seeking to cover up evidence of the government’s role in killings in the area.

The night before their deaths, Sharp and Catalán, accompanied by Tshintela, their local guide and translator, met with a group of militia members at the Woodland Hotel in Kananga.

During the exchange, which Catalán secretly recorded, the two experts sought assurances from the group’s leader that it would be safe to travel to the town of Bunkonde to interview civilians and militia leaders. A militia leader, Francois Muamba, speaking in Tshiluba, told them it would not be safe.

But two local Congolese men who translated Muamba’s remarks into French, José Tshibuabua and Thomas Nkashama, misrepresented his response, according to a transcript of the discussion prepared by U.N. police. Nkashama told Sharp and Catalán that Muamba offered to “guarantee your passage.”

Tshibuabua turned out to be an informant for the station chief for Congo’s National Intelligence Agency in Kananga, according to U.N. documents and a senior Congolese intelligence official. U.N. investigators were never able to obtain Nkashama’s phone number or trace his phone calls. But several months after the killings, Nkashama and Tshibuabua were given a job with Congo’s General Directorate for Migration, which is responsible for border control and is part of Congo’s security services.

The translator Sharp and Catalán hired for the meeting, Tshintela, did not correct the misperception. He, too, turned out to be a government informant, who communicated with a military intelligence officer regularly following his encounters with the two U.N. experts, according to U.N. documents and court testimony.

The officer, Col. Jean de Dieu Mambweni, is a powerful local figure in the Congolese military who was running the operation to infiltrate the region’s militias.

Mambweni’s phone logs, also viewed by FP, show he was in touch with many of the key players, including one of the suspected killers, Sharp and Catalán themselves, and their interpreter. On the day of the killing, 45 inbound and outbound calls were logged on his phone. One of those calls placed him at a cell tower on the road to the crime scene.

Congolese authorities have not brought charges against Mambweni, and they have not accused him playing any role in the murders. In court proceedings earlier this month, he said that his own phone was turned off on the day of the killings and in the days that followed. He also confirmed having been in contact with one of the murder suspects. The suspect, he said, was a government informant who disclosed the murders to him. When the informant fell under suspicion, Mambweni added, he arrested him and delivered him to the military prosecutor.

Efforts to reach Mambweni on his cell phone were unsuccessful. Mambweni’s lawyer, Tresor Kabangu, told FP that it was too early in the trial to determine if there was a conspiracy to kill the two U.N. experts. But he said that Mambweni had merely contacted one of the murder suspects as “part of his duty to inform the people about the murder.”

In an interview with Radio France Internationale and Reuters in December 2017, Mambweni confirmed that he had been in touch with Zaida and Catalán. But he hung up when asked whether he had been in phone contact with their interpreter, Tshintela.

Tshibuabua and Nkashama are in detention and unavailable for comment.

But Kabangu, who also represents Tshibuabua and Nkashama, said that the two men had not tried to mislead the two U.N. experts and denied any guilt. During their meeting with Sharp and Catalán, he said, the two men called an unidentified contact in the town of Bunkonde who told them it was safe to travel. “They didn’t hide anything; they didn’t have a bad intent in what they were doing,” Kabangu said. “They made a phone call and were told it was ok.”

In the days and months after the killings, Congolese authorities routinely misled U.N. investigators, falsely reported that Sharp and Catalán were alive, and tampered with witnesses. They also sought to ram through a military trial before the investigation had been concluded, the documents show.

Government forces “are clearly being obstructive with us,” one U.N. political officer complained in an email.

U.N. investigators grew increasingly worried that the military prosecutor was trying to short-circuit the investigation, possibly at the bidding of the Congolese government. Following a meeting on May 12, 2017, with the investigating magistrate, members of the U.N. task force (which worked independently from the U.N. Board of Inquiry) wrote in their report that “there is deplorably little seriousness” in the probe.

The prosecutor, the members noted, was ignorant of basic facts of the case. He couldn’t say when Sharp and Catalán had first arrived in Kananga or which hotel they had stayed in. He had made no effort to interview key witnesses, and when one suspect had escaped from prison, he did not have him arrested. The most compelling evidence—a copy of a video of the killing—had been handed to the prosecutor by the U.N.’s own investigators.

The report reflected the investigators’ concern that the military would “charge only a few people and camouflage the truth about the actual murders.”

“All of this just to hide the truth, which may involve the Congolese government,” members of the task force wrote.

The task force investigators fed their findings to Starr, the U.N. official who ran the Board of Inquiry—but Starr appears to have downplayed the evidence.

In a phone call with the Sharps before the release of his report, Starr said: “We don’t particularly believe the larger conspiracy theories going around that anybody in the government, you know, decided that Michael and Zaida, you know, could be killed,” he said. The Sharps shared a recording of the call.

Starr told the Sharps that while he was keen to apply pressure on the government to credibly investigate the crimes, a report that blamed the government would make it impossible for the United Nations to continue its own follow-up investigation.

“We’re running a fine blade here,” Starr told the couple. “We don’t want to make the report so bad that they [the Congolese government] cease cooperating.”

“There is a line I don’t want to cross in terms of implicating them or anything, because I think that would just stop the investigation,” he added.

In his final report, issued on Aug. 15, 2017, Starr did not rule out the possibility of a government role in the killing. But he gave greater weight to other theories.

Sharp and Catalán had stumbled into a predicament they scarcely understood, he told the Sharp family. What’s worse, they had recklessly disregarded security procedures that could have saved their lives.

“Please forgive me for this,” he told them. “I don’t think they either understood fully or considered fully the security implications of doing it.”

“I think they made a mistake,” he said.

But people familiar with the kind of investigation Sharp and Catalán were conducting said Starr showed little understanding of the work, which often required the experts to operate independently of the United Nations.

“So, yes, maybe we were taking excessive risks. That is possible, and that is a discussion we should have,” said Jason Stearns, an expert on Congo who previously served on a U.N. sanctions panel there. But “they were not killed because they were reckless. They got killed because somebody wanted to kill them.”

Some U.N. officials viewed the final report as an effort to shield U.N. brass from any responsibility for the deaths of Sharp and Catalán and maintain Congo’s support for the U.N. peacekeeping mission in the country.

“The U.N. kept running away from the truth, even if we had a clear indication from the start that the government was involved,” said one senior U.N. official. “The U.N. could not admit the government was involved—they would have to put an end to the partnership.”

After Starr submitted his report, U.N. Secretary-General António Guterres met with the families of Michael Sharp and Zaida Catalán at U.N. headquarters in New York. He pledged to establish an independent investigation if the Congolese authorities failed to conduct a credible prosecution. And he seemed to distance himself from the findings of the Board of Inquiry, according to Catalán’s family.

“[He] told us that it was a planned murder and it wasn’t Zaida and Michael’s fault, as indicated in the Board of Inquiry,” Elizabeth Morseby, Catalán’s sister, said in an interview.

“That was very nice for us to hear,” said Catalán’s mother, Maria Morseby.

But in response to written questions, the U.N. secretary-general’s office rallied to Starr’s defense. “There is nothing to suggest that Mr. Starr was less than truthful to the families,” wrote Stephane Dujarric, the chief spokesman for the U.N. secretary-general. “Mr. Starr’s briefings to the families was based on the evidence and materials that he had received through the course of activities.”

U.N. officials said the board of inquiry was never intended to conduct a full fledged criminal investigation. China and Russia made it clear they would oppose any initiative in the U.N. Security Council an independent investigation into the murders without Congolese consent. Despite the constraints, the U.N. mission in Congo played a critical role in identifying the remains of Sharp and Catalán, unearthing key pieces of evidence and helping the Congolese authorities locate suspects and witnesses.

The Board of Inquiry as “a vehicle that could guide me on proposing any changes on how the experts are managed, to prevent a repetition of these murders, and I don’t think that is an insignificant goal,” Feltman said.

Feltman said that he “certainly did want to see accountability for these two people, who were part of the U.N. family.” But his primary concern was “what in the world do we do to ensure we don’t have to call the other families of experts with similarly horrible news. What do we do in terms of safety procedures. Were there deficiencies in how we treated or trained the experts?”

Starr, responding to questions by email, vigorously defended his report. He also denied telling the Sharps he had referred the investigators as cowboys.

“I stand by what we said in the report. We are certainly not protecting anyone or hiding anything,” he wrote. “The BOI [Board of Inquiry] was administrative, not criminal, and time limited.”

“In regards to the families, we tried very hard to help them through this,” he added. “It must be incredibly difficult for them as the people identified in the video murdering Michael and Zaida have not been apprehended, much less anyone else who may be involved.”

Since that meeting, the families have had to pin their hopes on a team of U.N. lawyers who are trying to discreetly prod the Congolese military prosecutor into conducting a credible investigation and trial.

But the head attorney on the team, Robert Petit of Canada, has acknowledged that he has no authority to investigate the matter and “no juridical or legal powers.”

“We don’t have any jurisdiction in the DRC, we have no power, we’re not a prosecutorial entity, we’re not an investigative entity,” he added.

Back in January, Petit raised concerns about the lack of a commitment by Congo to conduct a credible investigation into the crime. Congolese security forces, he noted, have repeatedly intervened in the investigation, raising “concerns regarding possible interference with witnesses,” he wrote in a memo to Guterres, the U.N. secretary-general.

“The investigation conducted to date is far from complete and does not meet international standards of diligence,” Petit wrote. “For example, potentially relevant witnesses have not been summoned or interviewed, even though they appear available, and witness interview records are lacking in details.”

But Petit has assured the families that it’s worth pursuing the case. “I firmly believe that this case will eventually be solved. At the end of a trial, if it’s done properly, you have the truth, beyond a reasonable doubt,” he told Sweden’s Sveriges Television.

Ultimately, the course of justice may rest in the hands of a senior Congolese military prosecutor, Gen. Timothée Mukutu.

Mukutu has overseen some of the country’s most politically sensitive trials, including one case involving the mass killing of civilians in the northeastern city of Beni. Petit recently informed the Sharp family that Mukutu is expected to indict three suspects: Col. Jean de Dieu Mambweni, Thomas Nkashama, and José Tshibuabua, though it’s not clear what they would be charged with.

But Mukutu said he doubts that the crime would have been ordered by anyone in the Congolese government.

“Who profits from this crime?” he said in an interview with Sveriges Television. “What could have been the motive? The murder of two experts of the United Nations on Congolese land puts a heavy responsibility on the Congolese government.”

“I don’t see why the state would have organized these crimes,” he said.

That kind of remark reinforces concerns among human rights advocates that Mukutu will mostly try to protect the regime from judicial scrutiny.

“I think it’s highly unlikely that we’re going to get the full truth of what happened and that those ultimately responsible will be brought to justice,” said Ida Sawyer, an expert on Congo at Human Rights Watch. The concern with Mukutu “taking over this case is that he will work to ensure that any senior-level officials are protected.”

The Sharps are still hoping for an international investigation. But the convictions are less important to them.

“Even if somebody is indicted, imprisoned, sentenced to life imprisonment, or executed, that solves nothing. It’s more violence in response to violence,” said Sharp’s father, John. “There’s got to be something better. I’d like to think of some kind of restorative justice.”

In honoring Michael’s death, the Sharps decided against a traditional burial. Instead, they plan to spread his ashes in various parts of the world. They will scatter some at the top of Mount Kilimanjaro this March, on the second anniversary of his death, as part of a benefit for a scholarship fund at Eastern Mennonite University’s Center for Justice and Peacebuilding.

“[Michael] was a citizen of the world, and we could not possibly bury his body in one place,” John Sharp said.

Martin de Bourmont and Stéphanie Fillion contributed to this report.

This story was updated on November 27.