ex-KGB agents were in the most favorable position to participate in the power and asset grab after the collapse. They knew how things were run, they had the connections, they also were most educated and most trained. They sort of represented an elite class of individuals selected, educated and trained better than the rest.
When things fell apart a lot of them scattered looking to grab whatever as available. Political and patriotic allegiance to the party has become a running joke since after the 60s. Most of them had absolutely no problem switching practically overnight from staunch supporters of communism to brutal capitalists.
Back in late 80s and early 90s there was a mod and there was a FSB, with former comprised predominantly of criminals and former athletes. I am sure you are well aware of that if you lived in Russia at that time.
Some people think of local street gangs because they are just more visible, I am thinking of mobsters who were running the whole country. There were often connections between the two but both were operating at different scales and in different domains.