I highly recommend reading Bellingcat's investigation into the poisoning of Alexei Navalny and how they tracked down the individual FSB officers responsible:
https://www.bellingcat.com/resources/2020/12/14/navalny-fsb-...It's the most impressive investigative work I have ever read. One can only imagine the capabilities of nation state actors if an NGO is capable of this.
Even more incredible is that Alexei Navalny personally called an FSB officer and was able to extract a confession: https://www.youtube.com/watch?v=gwvA49ZXnf8
