I'm pretty sure there are court cases against these companies that hired them, there are also more interviews of Russians on video saying this stuff. You should look into that.
I would recommend looking at the years 2016 through 2019 , plus Facebook, Cambridge Analytica, and other companies like that. Europe recently talked about going after a company doing this stuff.
Here's a good portion of my bookmark vault: https://sh.itjust.works/post/33277983