© Sputnik/Alexei Druzhinin/Kremlin via REUTERS

Unit 29155, the Russian assassination squad operating with impunity across Europe, received diplomatic cover from the Russian mission in Switzerland.

Unfortunately, one of the main suspects relocated back to Russia before authorities could detain him.

"We were not thrilled that these activities hit the media when they did because we were watching some of these guys in hopes of identifying the unit and its members," an intelligence source told Insider.

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A secret unit of the Russian intelligence services accused of three killings or attempted assassinations across Europe and the UK, plus an attempted coup in Montenegro, has used diplomatic cover for operations around the continent, according to intelligence officials and open-source researchers who talked to Insider.

The revelation that "Unit 29155" has used diplomatic passports from the Russian mission in Switzerland brought new scrutiny by European intelligence services tracking the unit's operatives.

Unit 29155 is a unit of Russian military intelligence known by its Russian acronym GRU, which is a successor to the Soviet-era KGB

Members of Unit 29155 have been accused in attempted or successful assassinations in the UK, Germany, and Bulgaria. They are also suspected of politically destabilizing activities in Montenegro, Spain and Moldova. The unit is believed to be the home of an elite unit of former Russain special forces members tasked with eliminating Russia's enemies abroad and was specifically implicated in two poisonings - of a Bulgarian arms dealer in 2015 and in the 2018 poisoning of Sergei Skripal, a former GRU officer who defected to the UK, in Salisbury.

Unit 29155 became active in the aftermath of the 2008 Russian invasion of Georgia, according to NATO intelligence officials told Insider, who described a process of understanding the group's activities and mandate that took about a decade.

"In retrospect, we can pin the start of these sorts of activities to 2008 and the clash between Russia and Georgia over [the breakaway Georgia region of] Ossetia," said a NATO military intelligence official based in Brussels. "This era was the start of a range of very aggressive actions by Russian intelligence services that have only escalated since."

"But it can take some time for analysts to identify a new program of operations like we have seen from the Russians over the last decade, in this case it took until the situation in (2014) Ukraine and Crimea for NATO and its member services to really grasp the extent to which the Russians were embracing covert but very aggressive operations."

After Russia used covert operations, information warfare, and irregular troops to seize control of Ukraine's Crimea region in 2014, Unit 29155 started to ramp up operations inside the European Union, said the official.

"We started seeing brazenly strange incidents around key places beyond even the high-profile assassination stuff," said the official, who tracks Russian intelligence operations for a European country and cannot be named due to the nature of their work.

"There were information operations in (2015) Moldova, the (2015) poisoning in Bulgaria, an attempted coup in (2016) Montenegro, all very obviously linked to the Russians, the official said. "But it was hard to link it to one specific operation or unit until we identified that it was all being organized out of Switzerland under diplomatic cover."

Intelligence services determined that Unit 29155's activities were being coordinated by a Russian official working in Geneva with diplomatic status under the name "Georgy Gorshkov." In late February, open-source researchers at Bellingcat working alongside Russian and Swiss journalists determined that Gorshkov been coordinating the unit's activities since arriving in Switzerland in 2017.

According to research by Bellingcat and its local partners, Gorshkov, assigned to the World Trade Organization, is actually the cover name of a GRU officer named Egor Gordienko.

The NATO official confirmed Bellingcat's reporting that Gordienko was believed to have been closely involved in the Bulgarian and Montenegro operations before his posting to Geneva. Then, Bellingcat and its partners identified that a unit of Russian intelligence - later identified as Unit 29155 - was operating across Europe in 2018. After that, Gordienko was recalled to Moscow before his identity leaked.

"We were not thrilled that these activities hit the media when they did because we were watching some of these guys in hopes of identifying the unit and its members," said the official. "But Gordienko would have been kicked out after Salisbury anyway so the loss of information from the media wasn't that bad."