We have federal income taxes too. The US IRS will play the same sort of tricks for delinquent taxes (imagined and real).
I also spoke with IRS CID on another matter (someone was making death threats to IRS agents, and they had mail through my anon remailer). Way saner than FBI or even USSS. (I had no information, by design, but being able to tell someone that and explain how remailers worked without them threatening to seize servers was refreshing.)
Do you mind elaborating? I was under the impression that capital gains aren't taxed until they're realized, would love to hear when that's not the case.