Firstly, there should be abundantly more evidence than that is presented to ensure they are alts. And besides, if those alts of his are banned, there's no guarantee that he will not go ahead and create 5 more alts in a day and continue his activities. The most effective means to curb this is to report and possibly ignore if it persists.
I think Op feels there's no point in supplying 'abundant evidence ' when the whole thing is very clear. Even looking at the writing patterns of these other accounts and comparing it with the Polo7 one, you'd get your answer except you'd want to tell me they are probably different people, then I'd say the coincidence is just too much but then again like another user pointed out, instead of creating a thread for this, the best thing is to report to the moderators and if Op thinks it's pointless because this user has been freely flaunting his egregious behavior in this place without proper actions being taken on him. And that the only way is to make a thread that would somehow throw a shade at the accounts, then he too is also flooding the forum.