Thanks for your efforts to detect alt accounts. As a general forum member, I am pretty sure they are an alt account. But as a DT member, I won't tag based on the evidence that you presented here. Having alt accounts isn't a crime, but abuse & cheat with an alt account is a crime. So you may keep them on the eye to find more solid evidence that would help tag them. But I think they will be aware from now since accounts are already in question.