Well, no other way to entrap someone this way other than ruining your own account in the process. As I said in my previous post, I am more inclined to believe that those two accounts are indeed his. I mean, if those two accounts were like Newbie/Jr Member/Member then yes, someone could have wasted them just to ruin him,  but in this case situation is different and accounts were of decent rank which makes entrapment less likely. But still, forum staff is hesitant to ban anyone without proving beyond a reasonable doubt that it is the case of ban evading, and with them using the address after him that's not the case here.

Having said all this, bitcointalk has very capable investigators and if there is something to be found, it most likely will.