When a video showing the murders of two UN workers was aired last month in the Democratic Republic of the Congo, the government justified the move as necessary to prove local militia were behind the deaths.

The grim footage, which was shown to reporters in Kinshasa, shows the final moments before the shooting of American Michael Sharp and his Swedish colleague Zaida Catalán, who was then beheaded.

The pair had been working in the Kasai region of the country, where they were investigating the activities of the Kamwina Nsapu rebel group, which the government claimed was responsible for the killings.

Experts on the ground have urged the UN to carry out a more thorough investigation, however. They say the footage raises more questions than it answers and fails to rule out possible government involvement in the deaths.

A source working for an NGO told the Guardian: “The most important aspects of the video and the questions they raise appear to have been glossed over by the international community. For one [thing], it takes very little skill to analyse the language used.”

Grainy footage shot on a hidden camera shows the investigators walking with their killers and apparently at ease before they sit down in a clearing and a shot is fired, killing Sharp.

Off camera, orders to execute Catalán – “Tirer, tirer lisusu,” meaning “Shoot, shoot again” – are given in a mixture of French and Lingala. The pair are then filmed lying bloodied on the ground, before some of Catalán’s hair is removed and she is beheaded.

They are walking comfortably, their hands are not tied. They are not under the impression they are being held hostage

“The local militia, Kamwina Nsapu, speak Tshiluba but the orders are given in French and Lingala, the trademark language of the national army,” the expert explained.

“Michael has been shot and Zaida is getting up and running – it’s a high-stakes moment in which you would use the language that comes most naturally.”

The source, whose identity is being protected for safety reasons, said the film also proved the pair had not been kidnapped, as initially claimed by the government when they first went missing on 12 March this year along with their interpreter, Betu Tshintela. The bodies of Sharp and Catalán were discovered two weeks later.

“There was never a kidnapping – what the video shows is a set-up,” the source said.

“They are walking comfortably, their hands are not tied, Michael is asking questions about who they are to meet next and is clearly in evidence-gathering mode. They are not under the impression they are being held hostage.”

The source added: “It is vital the UN commits to a full investigation to establish the perpetrator.”

The men seen walking with Sharp and Catalán are wearing red headbands characteristic of the local Kamwina Nsapu militia, but experts say it would be rare for a militia in the area to film a crime in this way.

Phil Clark, a political scientist who specialises in conflict in Africa, says the DRC government has never before given such prominent coverage to atrocities allegedly committed by rebel groups.

“There is definitely something unusual going on here,” said Clark. “It seems very peculiar that a rebel group would film its own crimes, especially in such a high-profile killing. That is almost unheard of among Congolese rebel groups – in fact, it would be first in terms of tactics.

“If they were to do this for propaganda purposes, then why use a hidden camera? Why not distribute it themselves?”

Conflict specialists working in the region have suggested collusion between those working for the authorities and the local militia as another possible explanation.

One said: “It is part of the government’s regular modus operandi to work with rebels, and the Kamwina Nsapu is quite fragmented, with one branch closer to the government. They may have found some rogue members from the group – we just don’t know.”

However, Clark, who teaches African politics at Soas University of London, said that while it is a common tactic of Joseph Kabila’s government to use rebel groups as proxies for its own dirty work, it would be an unlikely move in this context.

“It would be hard to believe they had suddenly formed this kind of alliance in such a risky and high-profile attack, because tensions between the two sides have been running so high.”

Kasai was previously one of the more stable provinces in the DRC, but it has become a hotbed of opposition and a fulcrum of much of the discontent and rebel activity.

The conflict has escalated since last August, when security forces killed a local chief, Kamwina Nsapu, spawning the militia group of the same name.

Congo’s government is under pressure to investigate the violence in Kasai, where the UN says it has found about 40 mass graves.

After the execution video was aired, the government’s minister of communications, Lambert Mende, said the footage had been shot by the militia and secured by the police. The footage was posted online.



He told the media: “Our police and soldiers are accused of being implicated in the assassination of the two UN experts. That is not the case. The images speak for themselves.”

He added: “It is not our soldiers that we see in the video executing the two UN workers, but the terrorists of the Kamwina Nsapu.”

A statement from the DRC embassy in London said arrests have since been made in connection with the video. It added that the use of language was “not an indication of belonging to a particular category of people”.

It is understood that two other clips were also shown, including one featuring a large number of beheaded bodies wearing police uniforms. Again, authorities said the rebel group was to blame for the deaths.

When approached by the Guardian, Mende said: “It is a judicial case, so I can’t discuss it. The government did not distribute the images: rather, it was the prosecutor’s office.”

The Kamwina Nsapu have neither denied nor claimed responsibility for the murders.

The UN is under growing pressure to identify the perpetrators; insiders say talks on whether to conduct an internal investigation or carry out a wider inquiry into the murders are ongoing.

Last week, the UN’s high commissioner for human rights, Zeid Ra’ad al-Hussein, said the situation in the region was “deeply alarming”.

A spokesman for the UN in New York said that, though every incident involving casualties among UN staff is subject to internal investigation, the organisation – including its peacekeeping arm – does not have a mandate or jurisdiction to carry out criminal investigations.