Three Russian nationals killed in the Central African Republic late Monday are believed to be prominent documentary filmmaker Alexander Rastorguyev, cameraman Kirill Radchenko and journalist Orkhan Dzhemal. The Russian Foreign Ministry has confirmed that the men found dead about 300 kilometers from the capital of Bangui had ID cards on them bearing those names. The trio’s driver has told Reuters they were ambushed by armed men outside the town of Sibut.

Rastorguyev’s films have played at the Karlovy Vary and Cinéma du Réel festivals, among others. His credits include the 2014 award-winning doc Srok (The Term), about the opposition movement in Vladimir Putin’s Russia. Dzhemal was a leading military correspondent and Radchenko a former projectionist, according to reports.

The crew was looking into the activities of a private security company with murky ties to the Kremlin. The film project is backed by The Centre for Investigation, a news organization funded by exiled oil tycoon Mikhail Khodorkovsky who is a vocal Putin critic. In a statement on his own website, Khodorkovsky said he had “received an unofficial, but sufficiently strong confirmation that all three film crew journalists have been killed.” He confirmed the crew was working on an investigation into Russian private mercenaries, “in particular the Wagner group” and said, “These were brave men who were not prepared simply to collect documentary material, but wanted to ‘feel’ it in the palms of their hands.”

The Wagner group is an organization of private military contractors which sources have told Reuters carried out clandestine combat missions on the Kremlin’s behalf in eastern Ukraine and Syria.

The New York Times reported there was no indication the killings were related to the documentary and that Russian investigators have opened a criminal case to look into the deaths. Robbery has been floated as a motive in some reports.

Khodorkovsky added regarding the filmmakers, “I hoped until the last moment that they had been captured, and that they could be rescued… I will make efforts to identify the perpetrators.”