Ricin and the umbrella murder

Markov was hit by the dart after walking across Waterloo Bridge RELATED What is ricin? Ricin as a weapon

LONDON, England -- It was one of the most notorious acts of assassination carried out during the Cold War.

Bulgarian dissident Georgi Markov was killed by poison dart filled with ricin and fired from an umbrella in London in 1978.

Markov, a communist defector working for the BBC World Service, left his office at Bush House in the UK capital on September 11 and walked across Waterloo Bridge to take the train home to Clapham in south-west London.

As he waited at a bus stop moments into his journey home, he felt a sharp jab in his thigh and saw a man picking up an umbrella.

He developed a high temperature and in four days was dead.

A post mortem, conducted with the help of scientists from the UK government's germ warfare centre at Porton Down, established that he had been killed by a tiny pellet containing a 0.2 milligram dose of the poison ricin.

Markov's assassination was detected only because the pellet carrying the poison had not dissolved as expected.

His assassin has never been captured despite close cooperation between British and Bulgarian authorities, including Interpol.

Markov, a playwright and satirist who had broadcast scathing accounts of Communist high life to Bulgaria, was the subject of two failed assassination attempts before he was killed.

And in the years following his death efforts were made to reveal the chain of command which led to the order for his assassination being given.

KGB suspected in assassination

It is believed that the operation was supported by the technical staff of the Soviet KGB and seems to have involved many senior members of the Bulgarian secret police.

In June 1992 General Vladimir Todorov, the former intelligence chief, was sentenced to 16 months in jail for destroying 10 volumes of material on the case.

A second suspect, General Stoyan Savov, the deputy interior minister, committed suicide rather than face trial for destroying the files.

Another Bulgarian spy, Vasil Kotsev, who was widely believed to have been the operational commander of the Markov assassination plot, died in an unexplained car accident.

Scotland Yard says the case remains open.

Extracted from the seeds of the castor bean plant Ricinus communis, ricin is one of the most feared substances with the potential to be used as a bio-terror agent or weapon of mass destruction.

It is widely available, easy to produce, and a tiny amount is enough to kill an adult.