Kirill Radchenko, Alexander Rastorguyev and Orkhan Dzhemal were investigating the activities of a shadowy Russian private mercenary company, Wagner Group, which had reportedly set up camps in the country and is owned by a crony of Vladimir Putin. Three days later, the journalists were dead.

They were ambushed by gunfire on a remote road, at night. The facts are murky.

Official statements claimed they were attacked by robbers. But others have questioned why, once they began seeking answers about a secretive business connected to the Kremlin, they were shot and killed. Their driver escaped.

The Wagner Group, which also sent forces to Syria, was founded by Yevgeniy Prigozhin, the St Petersburg catering magnate who also owned the troll factory known as the internet Research Agency used to interfere in the 2016 United States presidential election.

The work of the three courageous journalists was being funded by the Investigations Management Centre, supported by exiled Russian oligarch Mikhail Khodorkovsky.

The three were experienced. Dzhemal was the former political editor of Novaya Gazeta, a hard-hitting investigative newspaper, and had covered wars in Georgia and Ukraine.

Rastorguyev was a director known for a documentary on the anti-Putin opposition. Radchenko was an accomplished photographer.

Khodorkovsky, who has become an outspoken critic of Putin's authoritarian regime, announced that he and his former business partner, Leonid Nevzlin, are setting up a $5 million foundation to investigate violence against journalists targeted as a result of their professional duties.

Sadly, the killing and imprisonment of journalists for their work is a scourge worldwide, including the wanton murders in the Capital Gazette newsroom in Annapolis, Maryland, on June 28.

This year alone, 39 journalists have been killed in the line of duty, compared with 46 in all of last year, according to the Committee to Protect Journalists.

Last year, the CPJ counted 262 journalists behind bars because of their work, and about half of all those were in just three countries: Turkey, China and Egypt.

While these authoritarian regimes are the worst, journalism has proved hazardous in many other locations, including Myanmar, where two Reuters reporters have been sentenced to seven years in prison for their revelatory digging into the brutal exile of the Rohingya Muslims, and Venezuela, where some 70 newspapers, radio stations and television outlets were forced to close last year.

To deter more killings and jailings, it is essential that every case be exposed and those who ordered the abuses be held to account.

At its very heart, this violence is aimed at not only the reporters but also their readers and viewers in an attempt to hide vital truths and silence the voices that convey it.

Censorship is a corrosive tool in the black arts of dictators and autocrats, and violence against journalists is an extreme expression of their determination to smother the truth.