Agents of the Bulgarian secret police (Darzhavna Sigurnost; Bulgarian: Държавна сигурност, abbreviated ДС), assisted by the KGB, had previously made two failed attempts to kill Markov before a third attempt succeeded. On September 7, 1978 (the 67th birthday of Todor Zhivkov), Markov walked across Waterloo Bridge spanning the River Thames, and waited at a bus stop to take a bus to his job at the BBC. He felt a slight sharp pain, as a bug bite or sting, on the back of his right thigh. He looked behind him and saw a man picking up an umbrella off the ground. The man hurriedly crossed to the other side of the street and got in a taxi which then drove away. The event is recalled as the "Umbrella Murder" with the assassin claimed to be Francesco Gullino, codenamed "Piccadilly".
When he arrived at work at the BBC World Service offices, Markov 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. He told at least one of his colleagues at the BBC about this incident. That evening he developed a fever and was admitted to a hospital where he died three days later, on September 11, 1978, at the age of 49. The cause of death was poisoning from a ricin-filled pellet.
