LONDON, England (CNN) -- British detectives have launched a fresh probe into the umbrella assassination of Bulgarian dissident Georgi Markov nearly 30 years ago, according to reports.
Markov, a communist defector working for the BBC World Service, is believed to have been stabbed with the poisoned tip of an umbrella filled with the toxin ricin in September 1978.
The British Press Association reported police had recently visited Bulgaria three times to try and track Markov's killer(s).
A team of Metropolitan Police officers traveled to Bulgaria in April 2007, then in March this year and again last month to pursue leads in the case, PA reported.
British authorities have long suspected KGB staff and Bulgaria's secret police of involvement in Markov's death.
The Bulgarian newspaper Dnevnik reported that British police had requested access to archive files and permission to interview about 40 witnesses.
The detectives' activity was triggered by the fact that under Bulgarian law the 30-year statute of limitation on the case expires in September, the newspaper said.
A Scotland Yard spokeswoman quoted by PA said: "A small team of Metropolitan Police officers traveled to Bulgaria in May in connection with the inquiry into the death of Georgi Markov in 1978.
"The inquiry remains open and has been a particularly complex investigation. We continue to work with the appropriate authorities to investigate any new information that is passed or made available to police."
She told PA that officers periodically reviewed the case and had previously been given access to Bulgarian investigators' files.
Markov was poisoned while waiting at a bus stop in central London on September 11, 1978.
While standing there he felt a sharp jab in his thigh and saw a man picking up an umbrella. He died three days later.
A post-mortem examination, conducted with the help of UK germ warfare scientists, established he had been killed by a tiny pellet containing a 0.2mg dose of ricin.
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 finally killed.