SOFIA (Reuters) -- Bulgaria is closing its probe into a Cold War killing, the murder of dissident Georgi Markov in London, but an investigator said no evidence existed to back up the theory that he was stabbed with a poison-tipped umbrella.
Under Bulgarian law, the 30-year statute of limitations on the case expires on September 11, the anniversary of Markov's death, but Sofia will continue to work with British police on their investigation into the case.
Markov, a writer, journalist, and opponent of Bulgaria's former communist regime, died on September 11, 1978, after a stranger shot a ricin-laced pellet into his leg on London's Waterloo Bridge.
Luchezar Penev, head of Bulgaria's Serious Crimes Investigation unit, told Reuters that the popular story that an umbrella was used to inject the poison had not been confirmed.
"The famous umbrella is for someone who is writing a book...there is no evidence for such a thing," he said.
"The pellet's size was several times smaller to contain the necessary quantity of ricin, if we accept it's ricin, needed to kill a man," he added but declined to give any other details.
According to accounts of the incident, Markov, who defected to the West in 1969, was waiting for a bus when he felt a sharp sting in his thigh. A stranger fumbled behind him with an umbrella he had dropped and mumbled "sorry" before walking away.
Markov died four days later of what is believed to be ricin poisoning, for which there is no antidote.
British police are still eager to solve the murder.
Bulgaria's closure of the case coincides with the release of communist-era secret police files by the Bulgarian daily "Dnevnik" on September 8 that identified Markov's suspected assassin as an agent code-named "Piccadilly."
The files show how the agent underwent "special training" from Bulgaria's notorious secret police, Darzhavna Sigurnost, and received two medals, several free holidays, and $30,000 after Markov's death, "Dnevnik" reported.
The files, which "Dnevnik" said were incomplete, unveiled that Markov's case was discussed with the KGB in Moscow.
In the archives, Dnevnik said it had also found a secret agreement between Sofia and Moscow signed in 1972, under which the KGB was due to provide fast-acting poisons and devices for their delivery to Bulgarian intelligence.
"Dnevnik" journalist Hristo Hristov obtained the files after winning a court battle with the intelligence services, which had blocked his access to the archives. He said it was not clear whether Bulgaria had provided the files to British police.
Bulgaria has been among the last former Soviet bloc countries to deal with its painful past and in late 2006 passed a law to open the files of the much feared Darzhavna Sigurnost.