SOFIA -- Bulgarian officials say an investigation into the attempted assassination of an arms maker is focusing on five suspected Russian agents -- including a Russian military intelligence general alleged to have commanded a team accused in the 2018 Novichok attack in Britain against former Russian spy Sergei Skripal.
Authorities in Sofia also confirmed that they are working with the FBI and British medical experts to investigate the two suspected Russian poison attacks in 2015 in Bulgaria against Emiliyan Gebrev, owner of the weapons manufacturer EMCO Ltd.
Evidence about Denis Sergeyev, the purported operational commander behind the March 4, 2018 poisoning of Skripal and his daughter Yulia, was uncovered earlier this year by the British-based open-source investigative group Bellingcat.
Bellingcat identified Sergeyev as a major general from an "elite overseas clandestine-operations" team that is part of Russia's GRU military intelligence unit 29155.
Bellingcat confirmed that Sergeyev -- who visited Britain under the false identity of Sergei Fedotov at the precise time Skripal was targeted -- arrived in London two days before the failed assassination attempt.
Sergeyev left Britain on the afternoon of March 4, 2018 -- only a few hours after the front door handle of Skripal's Salisbury home was sprayed with the military-grade nerve agent Novichok, allegedly by two other Russian military intelligence agents who also traveled to Britain under false names.
Sotir Tsatsarov, who stepped down as Bulgaria's prosecutor-general on December 11 to head the country's anti-corruption committee, says investigators have confirmed that Sergeyev also traveled to Bulgaria three times in 2015 using the same false identity, Sergei Fedotov.
Tsatsarov said Sergeyev's Bulgarian travels coincided with the poisoning of Gebrev, his son Hristo Gebrev, and EMCO Production Manager Valentin Takhchiev -- all of whom survived the attacks.
"Through the international exchange, data on the identity of the suspects in the United Kingdom assassination attempt against Sergei and Yulia Skripal has been obtained," the Bulgarian Prosecutor-General's Office said.
"From the comparisons made in the databases of Bulgaria's Interior Ministry and the State Agency for National Security (SANS), one of them -- Sergei Fedotov -- was found to have visited Bulgaria three times in 2015," it said.
"His second visit was with entry on April 24, 2015 [at the coastal Burgas Airport] and with his departure on April 28, 2015" from Sofia Airport, Bulgarian investigators revealed.
The announcement officially confirms a key finding by Bellingcat that places Sergeyev in Bulgaria and Britain at precisely the times when the attacks against Gebrev and Skripal occurred.
"At the heart of the Bulgarian poisoning operation was a team of as many as eight GRU officers -- all members of the same unit -- who traveled to Bulgaria in the weeks surrounding the poisoning attempt," Bellingcat wrote in a joint investigative report with Germany's Der Spiegel and The Insider, published on November 23.
"Crucially, constellations of teams of three – including Major General Denis Sergeyev -- were present in Bulgaria" during both attacks on Gebrev, Bellingcat concluded.
Sergeyev's "elite overseas clandestine-operations unit" has also carried out numerous other secret operations in Europe, the joint investigative report found.
In the investigation by Bulgarian authorities, Tsatsarov said the British experts were examining medical samples taken in 2015 from Gebrev and his son to determine what poisonous substance was used against them.
Bulgaria's initial 2015 investigation was closed without finding evidence of any substance that has been banned by the Chemical Weapons Convention (OPCW).
But Novichok was a relatively unknown chemical warfare agent until the failed 2018 attack on the Skripals.
Gebrev tells RFE/RL that he called for Bulgaria's investigation to be reopened in 2018 after he noticed similarities to his symptoms and media reports about the reaction that Skripal and his daughter had after being exposed to Novichok.
He also is critical of Bulgarian officials who conducted the initial investigation into his poisoning.
"When the state wants to investigate, then it can," Gebrev told RFE/RL. "And when it doesn't want to, well, here it is 2019, four years later, and only now are they trying to understand what happened."
In October 2018, Tsatsarov signed an agreement with Bulgarian Interior Minister Mladen Marinov and SANS Chairman Dimitar Georgiev to create a special investigative team that reopened the Gebrev case.
"We are working in a joint team and a close partnership, and we are going to find out the facts in this case," British Ambassador to Bulgaria Emma Hopkins said in February, noting that the two countries had been "closely" coordinating their efforts for "several months."
Tsatsarov now says the British experts involved in the case have not yet disclosed whether Novichok was used against Gebrev.
Meanwhile, he says FBI agents are examining video recorded in April 2015 by security cameras in a parking garage beneath EMCO's Sofia headquarters.
State prosecutors say Sergeyev and several other Russian citizens that the investigation is focusing on stayed in a hotel near that building and had requested at least one room with a view of the entrance.
"It was found that some of these persons used accommodation in a hotel immediately next to the building where the office of EMCO Ltd. was located in 2015 with an explicit insistence on a specific room that provided direct observation of the entrance to the underground parking of the building," the prosecutor's office said.
Bulgarian investigators say they've also identified "a significant portion" of the travel routes, credit cards, phones, and cars used by the Russian suspects.
They say "one of the versions" of a motive for the Kremlin to order an attack against Gebrev is related to arms deliveries to Ukraine in December 2014 and January and March of 2015.
The Kremlin has disputed the findings of Bellingcat that implicate Russian GRU agents in Gebrev's poisoning.
It also denies involvement in the poisoning of the Skripals, which led to a series of sanctions against Russia by the West and tit-for-tat diplomatic expulsions.
Aleksandr Mishkin and Anatoly Chepiga -- two GRU colonels who traveled to Britain in March 2018 under the false identities of Ruslan Boshirov and Aleksandr Petrov and are accused by Britain of poisoning the Skripals -- have denied any involvement.
They have claimed they were traveling vitamin salesmen who visited Salisbury on the day of the Novichok attack to view its famous 14th-century cathedral spire.
That claim is mocked by residents of Salisbury who note that the cathedral is the first thing Mishkin and Chepiga would have seen upon their arrival in the medieval city as they passed through the Salisbury train station's only exit door.
Instead of walking toward the cathedral, CCTV footage shows the two Russian GRU agents went down a street in the opposite direction at the time of the Novichok attack to reach the neighborhood where Skripal's home was located.
Meanwhile, Bellingcat's analysis of data from Sergeyev's phone indicates that he communicated with officers in Moscow during his three-day stay at a hotel in London -- using 4G and 3G rather than open WiFi networks to connect to the Internet -- hundreds of times.
Bellingcat says the Russian GRU general's use of secure messaging apps like WhatsApp, Viber, and Telegram could have been used to communicate with Mishkin and Chepiga.
The British-based investigative website also concluded that Sergeyev's cellphone data shows he only left his hotel once during his three-day stay in Britain -- walking around central London during a 40-minute window on March 3 when he could have met Mishkin and Chepiga to give them the Novichok that was used to poison the Skripals the next day.