This is one example of how negative seo plays out. Get used to it because it is only getting worse. If they are not bombing your site with junk links, they are removing your good links. Either way your positions will probably drop in 3-4 weeks, if not sooner.
Good luck finding out who this person is. They often hide behind a proxy, use unidentifiable email accounts and are like anonymous ghosts moving from one victim to the next.