hm. that’s a sticky question.
first off, at the very least i would recommend contacting the people you already know offline and letting them know about your experience. that’s private communication, and there shouldn’t be any issue there; i would say you’re almost obliged to do at least that.
as for posting something to the list… i can see pros and cons. first off, do you know of anyone else who would be willing to corroborate your statements? is there anyone else on the list who worked with you and him at the old place? if it’s not just you speaking up, it makes it look a lot less like a personal vendetta and a lot more like a “valid complaint” (whatever that means). if you can get in touch with anyone who can back you up, contact them ahead of time and ask them to post to the list shortly after they see your message.
also - how much of a reputation do you have on this list? do most people recognize your name, or are you a lurker? the more of a public rep you have, the more weight your word is likely to carry.
be aware that depending on what you say on-list, the guy may respond. difficult as it may be, you’ll need to make it clear in your original posting that you have the moral high ground, which means, well, not saying mean things about the guy, and maintaining as clinical a tone as you can manage. be specific about dates and times, e.g. “I worked with Individual X from Date Y to Date Z. During this period of time, he repeatedly exhibited Behaviors A, B, and C. He was eventually terminated by Manager M with cause. As such, I would recommend that others exercise caution before entering into a working relationship with X and that anyone considering such a relationship communicate with X’s superiors concerning these issues.”
if he’s a real asshole, be prepared for him to call you a liar, to impugn any aspect of your character or personality, and so on and so forth. the more restrained and professional you are in your statements, the worse he looks if he gets ugly. if he sends you a nasty email in private, then you’ve really hit the jackpot; post it to the list and let it speak for itself.
in conclusion; i figure you should be able to warn individuals offline without it causing a massive headache. if you do decide to make a public statement, there are ways in which you can do it that put you in a strong position from the start and can minimize grief for you.