https://www.bbc.com/russian/media-58806474
https://www.rosbalt.ru/blogs/2021/10/14/1926168.html
https://lansinginstitute.org/2021/10/12/russian-intelligence-focus-in-bulgaria/
https://carnegie.ru/commentary/85526
http://region.expert/newpeople/
https://www.rosbalt.ru/blogs/2021/10/06/1924700.html