By Wednesday afternoon, most of Arkady Babchenko's friends and colleagues had gone through the familiar cycle of grief and confusion that follows the killing of a Russian dissident journalist.

Obituaries had been written, travel arrangements were in train for the funeral, and Western politicians including Boris Johnson had announced they were "appalled".

Meanwhile, Ukraine had blamed Russia, Russia had blamed Ukraine, and both launched rival investigations to prove their stories.

And journalists in both countries, taught by bitter experience not to trust official probes into the deaths of their colleagues, pledged to run their own investigations.

But then came a twist that no one could have predicted: Vasily Gritsak, the head of Ukraine's Security Service (SBU), called a press conference and announced the whole thing had been a hoax.