Story has just broken; little information available. Ignorant commentators are already pointing fingers at local Muslims, but my gut feeling would be the "militia" types in the area: I heard a lot of scary stuff from them on the radio when I lived there; and some of the circle behind the Oklahoma City bombing came out of there, as well as the "Huttaree" group arrested for terrorist plots some time ago.
Meh. Apparently (though no arrests yet) it was just about a messy divorce that he happened to be a lawyer in.