The cost of speaking out The not so mysterious deaths of Putin's opponents

The attacks have varied, from underwear tainted with the nerve agent Novichok or polonium-laced tea to the more straightforward assassinations by a bullet but, throughout Vladimir Putin's 23-year rule, Kremlin critics, journalists and defected spies have been killed and targeted for opposing him.

- Pjotr Sauer

The crash of Yevgeny Prigozhin's private jet, killing the warlord who spearheaded a mutiny against Russia's top army brass two months earlier, has added a new method to the Kremlin's extensive assassination menu.

While the Kremlin has insisted it was "a complete lie" that it had anything to do with the jet crash, Prigozhin's longstanding feud with the military and the armed uprising he led in June would give the Russian state ample motive for revenge.

Poisoning

Russian intelligence officials have turned political poisonings into something of an art form. Soviet scientists are believed to have worked for decades to develop colourless and odourless poisons.

While poisoning may seem like an archaic way to kill, observers have countered that it offers the advantage of being a discreet method of assassination. It can be carried out without immediate detection, allowing the perpetrator to escape the crime scene while offering plausible deniability to the Kremlin.

The two crimes that have most closely associated Putin with poisoning occurred in the UK.