17 January, 2007 - Published 14:28 GMT
The murder of a Bulgarian Service journalist Georgi Markov in 1978 sounded like a cross between an Agatha Christie detective story and a John le Carré spy novel.
Markov was killed at a bus stop in the middle of London, almost certainly because he was a strong critic of the Communist regime in his homeland.
The murder weapon was intriguing. It is believed to have been a poisoned umbrella.
Georgi Markov was a successful novelist and dramatist in Bulgaria before he defected to the West in 1969.
A play he had written, The Man Who Was Me had just been performed and upset Communist Party officials.
He fled to Italy, but in 1971 moved to London, where he worked for both the BBC at Bush House, the German broadcasters Deutsche Welle and for the American-run Radio Free Europe (RFE), where he was a weekly contributor.
Zhivkov orders "neutralization"
Well before his killing he was a marked man. In 1972, he was tried in his absence by a court in Sofia and sentenced to six-and-a-half years’ jail for "working for foreign organizations to undermine his own country".
But this only seemed to make him even more critical of the Bulgarian regime.
His broadcasts for RFE included a series of satirical programmes called Personal Meetings with Todor Zhivkov.
Zhivkov was the Bulgarian leader and not a man to upset. In 1977, he signed an order that allowed “all measures” to be used "to neutralize enemy emigres."
The fatal attack was carried out on 7 September, 1978 - Zhivkov’s birthday.
Murder at Waterloo
That day, Markov was coming to work at Bush House and heading for a bus stop on the south side of Waterloo Bridge over the River Thames.
It was lunchtime and the pavement was crowded. He said later that he suddenly felt a pain in his right thigh and when he turned round, saw a man picking up an umbrella.
The man apologized in a foreign accent and quickly got into a taxi. Markov went to work at Bush House, but later became very ill and the next day went to hospital.
Doctors found he had a small puncture wound in his thigh and diagnosed blood poisoning. Three days after the stabbing, he died.
A post mortem examination found a tiny pellet in his thigh, about one and a half millimeters wide. Two minute holes had been drilled in it, in which a powerful poison could have been kept.
Experts believe the poison was the highly toxic ricin.
After the fall of the Soviet Union it was learned that the Russian secret service, the KGB, had developed an umbrella that could inject ricin pellets into a victim.
Two former KGB officers who defected said their organization assisted in the murder, although it was carried out by an Italian criminal codenamed Piccadilly.
In 1997 the new elected Bulgarian President, Petar Stoyanov promised Britain to use all his powers to solve the case.
No one has ever been brought to justice.