After relocating to London, he worked as a broadcaster and journalist for the BBC World Service, the US-funded Radio Free Europe and West Germany's Deutsche Welle.

Markov used such forums to conduct a campaign of sarcastic criticism against the incumbent Bulgarian-Soviet regime, which, according to his wife at the time he died, eventually became "vitriolic" and included "really smearing mud on the people in the inner circles.

[2] Contemporary newspaper accounts reported that he had been stabbed in the leg with an umbrella delivering a poisoned pellet, wielded by someone associated with the Bulgarian Secret Service.

[3] Annabel Markov recalled her husband's view about the umbrella, telling the BBC's Panorama programme, in April 1979, "He felt a jab in his thigh.

Markov also wrote a number of plays but most of them were never staged or were removed from theatre repertoire by the Communist censors: To Crawl Under the Rainbow, The Elevator, Assassination in the Cul-de-Sac, Stalinists and I Was Him.

Markov was one of the authors of the popular TV series Every Kilometer (Всеки километър or At Every Milestone) which created the character of the Second World War detective Velinsky and his nemesis the Resistance fighter Deyanov.

Lies and truths swap their values with the frequency of an alternating current...We have seen how personality vanishes, how individuality is destroyed, how the spiritual life of a whole people is corrupted to turn them into a listless flock of sheep.

In 2000, Markov was posthumously awarded the Order of Stara Planina, Bulgaria's most prestigious honour, for his "significant contribution to the Bulgarian literature, drama and non-fiction and for his exceptional civic position and confrontation to the Communist regime."

[16] When he arrived at work at the BBC World Service offices, he noticed a small red pimple had formed at the site of the sting he had felt earlier and the pain had not lessened or stopped.

[citation needed] Bernard Riley, the physician treating Markov, considered many possible causes of his illness, including that he had been bitten by a venomous tropical snake.

[18] Due to the circumstances and statements Markov made to doctors expressing the suspicion that he had been poisoned, the Metropolitan Police ordered a thorough post-mortem of his body.

[19] Ten days before the assassination, an attempt was made to kill another Bulgarian defector, Vladimir Kostov, in the same manner as Markov, in a Paris Métro station.

[21] A British documentary, The Umbrella Assassin (2006), interviewed people associated with the case in Bulgaria, Britain, Denmark and America, and revealed that Gullino was alive and well, and still travelling freely throughout Europe.

Markov's assassination is mentioned in season two, episode seven of CSI: Crime Scene Investigation, by a character as he describes people poisoned with ricin to Gil Grissom.

[24] Markov's assassination is also mentioned in the neo-Western crime drama series Breaking Bad, season two, episode one, "Seven Thirty-Seven" as Walter and Jesse think of plans to kill Tuco Salamanca.

The character, Lt Hutton, is working on a classified program at the Naval Info-Ops Centre (NIOC) and is discovered to have been murdered using the same method as Markov, leading to a Soviet KGB plotline.

The assassination served as inspiration for a similar poisoning by KGB agents utilising an umbrella, in the period spy drama The Americans, in the second episode of the first season, The Clock.

German police – who noted a resemblance to the Markov case – analyzed the syringe which the victim had managed to take from the perpetrator, and found dimethylmercury;[27] the reported cause of death was mercury poisoning.

[28][29][30] In 2016, police in Chennai, India solved three separate murders when the four killers confessed to having used an umbrella tipped with a potassium cyanide-filled syringe.