I would retract and contact the moderator regarding your suspicion. See http://lesswrong.com/lw/kza/meta_new_lw_moderator_viliam_bur/
I already contacted Viliam_Bur with this suspicion a few months ago, and I doubt I'm the first. I'm assuming Viliam either doesn't feel he has sufficient evidence to act, doesn't feel that any action is warranted, or is too busy to follow up on this at the moment.
Yvain's comment below is a new piece of (fairly conclusive) evidence. Maybe that will impact the situation if Viliam felt he had insufficient evidence previously, so it might be worth drawing his attention to this thread.
I know this reeks of witch-hunting, but... I have a hunch that u/Eugine_Nier is back under the guise of u/Azathoth123. Reasons:
I don't have an axe to grind against the guy, I've only spoken to him a couple of times and didn't notice any particularly large karma hits afterwards, I just really dislike it when someone skirts the rules like that. Disruptive users evading permanent bans never helped any community ever.
Obviously I'm posting this here because I think a moderator should look into the matter. Usually I would be posting a disclaimer of some sort, apologizing in advance to Azathoth123 for attacking his standing with slanderous accusations if this turned out not to be the case. Well, I won't. The more I look into the matter, the more confident I get that they're the same person. Azathoth, if you're reading this and you're not Eugine_Nier, then I strongly advise you go search for your twin brother, I think you'll get along very well. Seriously, I'm saying this in good faith. You have a suspiciously great deal of things in common.
If retributive downvoting is (still) a concern (if not, then disregard this paragraph): I'd like to request, if such a thing is possible, that a mod karma-blocks me until the issue is over, so as to not incur undeserved downvotes (it would also mean I'd get no upvotes). In turn, I promise not to abuse the system by spamming the boards with garbage without consequences, but then again given my history so far on LW I don't think that such an abuse should be expected from me. For the record, I could have made a throwaway account just to say this, and not risk being karmassassinated, but 1) a zero karma account has no credibility and 2) for signalling reasons I prefer to put my money where my mouth is.
P.S. I only made this announcement its own post because the latest open thread was about to "expire".