The journalist, Arkady Babchenko, made global headlines last month when he appeared in public to reveal that his death had been staged.

In an interview with the BBC, Oleksiy Tsymbaliuk, a Ukrainian former priest, says he alerted security services as soon as a compatriot, Borys Herman, asked him to kill Mr Babchenko.

Officials staged the journalist’s death and some politicians blamed Russia.

Mr Babchenko, 41, is an open critic of Russian President Vladimir Putin and the Kremlin. Relations between Ukraine and Moscow are difficult — in 2014, Russia violated international law by annexing Crimea, and it continues to aid armed militias in eastern Ukraine.

In an interview with the BBC, Mr Tsymbaliuk detailed his involvement in Mr Babchenko’s mock death.

He was reportedly approached by Mr Herman in early April assassinate Mr Babchenko.

Mr Tsymbaliuk says he thinks he was chosen because Mr Herman, a weapons manufacturer, thought he could be “easily manipulated”.

Yet as soon as Mr Tsymbaliuk was asked to kill Babchenko, he alerted the Security Service of Ukraine (SBU), who agreed to stage a fake assassination of the journalist with Mr Tsymbaliuk as the fake assassin.

The SBU said it staged Mr Babchenko’s murder in order to arrest Ukrainian assassins, allegedly recruited by Russian security services operatives, who were actually planning on killing Mr Babchenko.

Several days before the staged killing was due to take place, Mr Tsymbaliuk met his supposed target for the first time at Mr Babchenko’s apartment.

“A [security service] operative introduced us to each other with the words ‘say hello to your possible murderer’,” Mr Tsymbaliuk told the BBC. “I told him: ‘You don’t get a chance every day to do a slap in the face of Putin.’”

Then, on May 29, the staged murder was enacted, with Mr Tsymbaliuk playing along as if he was a real assassin, in case he was being tracked.

“I finished my soup, called a taxi and I went to kill Babchenko. [At the apartment, Mr Babchenko] was lying on the floor in a pool of blood, waiting for the ambulance to arrive. I wished him good health and he asked that I not make him laugh,” he said.

Mr Tsymbaliuk was next escorted to a safe house, where he watched news of Mr Babchenko’s death filter through on social media.

Later that night, he messaged Mr Herman with the words “the parasitic worm is dealt with”, as if he had actually killed Mr Babchenko.

In the early hours of the morning a reply came through from Mr Herman requesting that they meet.

Yet, tipped off by Mr Tsymbaliuk, the SBU moved in to detain Mr Herman, who had been preparing to leave Ukraine.

As things stand, Mr Herman does not deny plotting with Mr Tsymbaliuk, but claims he knew that the assassination would be staged.

He also claims he was working with the SBU all along.