A Ukrainian national has been detained in Bulgaria who the prosecution believes to have masterminded the attack against former security agent Alexei Petrov, the Bulgarian National Television has said.
Interior Ministry sources cited by other media outlets suggest several Ukrainians have been arrested as well in relation to the case, but the number is not specified.
A grenade launchers attack not far from the center of Sofia occurred in October of last year, with Petrov launching his own investigation into the affair to help authorities.
Alexei Petrov, who had formerly worked for the Specialized Squad for Combating Terrorism, was exposed in 2008, by then Interior Minister Rumen Petkov, as an undercover agent at the State Agency for National Security, Bulgaria's domestic security and counter-intelligence service.
In the 1990s, he was involved in the insurance business, which at that time was notorious for the blackmailing practices used by some companies to "attract" customers. Until 1998, he had a share a security company along with Boyko Borisov, now Bulgaria's Prime Minister.
For some years he was facing a trial over allegedly having organized and been a member of an organized criminal gang.
The Octopus trial was set to continue in May of last year, but after the detention and subsequent administrative action against Rumyana Chenalova, the judge who was in charge of the case, it was again put on hold.