“Just as machine guns cannot be owned by civilians in this country ...” Not true. It is a pain in the butt (on purpose),but legal.http://www.thefirearmblog.com/blog/2014/05/21/machine-guns-legal-practical-guide-full-auto/ BTW, There are only 3 known incidents of legally owned full auto firearms being used to commit a crime since 1934, one of which was a murder committed by a LEO. http://www.guncite.com/gun_control_gcfullau.html (about half way down the page)
I am going to guess another was by someone who knew how to construct his very own ak47?