Bulgaria Reopens Poisoning Case, Citing Possible Link to Russia and Skripal Attack - The New York Times
https://www.nytimes.com/2019/02/11/world/europe/bulgaria-poisoning-russia-skripal.html
Finger Pointed at Russians in Alleged Coup Plot in Montenegro - The New York Times
https://www.nytimes.com/2016/11/26/world/europe/finger-pointed-at-russians-in-alleged-coup-plot-in-montenegro.html
How a Poisoning in Bulgaria Exposed Russian Assassins in Europe - The New York Times
https://www.nytimes.com/2019/12/22/world/europe/bulgaria-russia-assassination-squad.html
Russia’s Clandestine Chemical Weapons Programme and the GRU’s Unit 29155 - bellingcat
https://www.bellingcat.com/news/uk-and-europe/2020/10/23/russias-clandestine-chemical-weapons-programme-and-the-grus-unit-21955/
Senior GRU Leader Directly Involved With Czech Arms Depot Explosion - bellingcat
https://www.bellingcat.com/news/2021/04/20/senior-gru-leader-directly-involved-with-czech-arms-depot-explosion/
Top Secret Russian Unit Seeks to Destabilize Europe, Security Officials Say - The New York Times
https://www.nytimes.com/2019/10/08/world/europe/unit-29155-russia-gru.html