Can you think of a way that talking to the police might be different from posting on HN when it comes to self-incrimination? If you truly can't just let me know and I'll give you a hand, but you should try the exercise yourself first.
Thanks for the clarifying question, instead of an attack. I mean that anything you say that is publicly accessible can be used against you. Consider that you are charged with, I don't know, theft of a Coke. And you have a twitter account where you say you love Coke so much, but hate that its so expensive. This could very well be used against you, as it goes to a general motive. In the same way, HN discussions are wide ranging and could be used by a prosecutor in a similar way. And indeed, just posting here at all on a site with "hacker" in its title is inherently risky.
Unless you use your real name and really start mouthing off, this isn't really the kind of network the DA is going to start shooting off subpoenas to....unless you Enron...