https://lansinginstitute.org/2021/10/12/russian-intelligence-focus-in-bulgaria/
https://www.rbc.ru/newspaper/2021/10/04/6157139c9a79478b74d9a463
https://www.kp.ru/daily/28335.5/4480309/
https://www.radiosvoboda.org/a/dopovid-oon-pro-prava-ludyny/31475103.html
http://www.kasparov.ru/material.php?id=614AC17983B54§ion_id=43452FA6D4743
https://www.nytimes.com/2021/09/19/opinion/putin-russia-election.html