Northwest Arkansas Morning News reports
The defense tried to make the case an issue of the Constitution versus federal gun laws. The government tried to make the case as simple as possible for jurors — Fincher had the machine guns and they weren’t registered as required by federal law.
Wrong, actually.  The defense was not allowed to make such a case, because the "judge" decided that the Second Amendment of the Constitution had no place in a court of "law."

David Codrea makes the same point about a different article from AP.