It didn't take long. Just heard on my radio (I forget the affiliate - CBS?), at the top of the hour news, that according to an unnamed Wisconsin "official", it might have been because of the recent repeal of the so-called "Assault Wepaon Ban".
Fact:
This "feel-good" law was NOT repealed. It expired and was not reauthorized by Congress. By a wide, bi-partisan margin. Read the link.
http://www.factcheck.org/article258.html