Were those weapons legally purchased? Roughly the lowest price for a fully automatic firearm is $10,000. And for each purchase you have a several month long waiting period for the federal, state and local background checks to take place before your two hundred dollar tax stamp for each firearm is issued.
A quick search provided this list of disqualifiers to own about any firearm, but especially fully automatic ones.
If the person is a felon, has been convicted of any crime punishable by more than a year in prison whether or not they were ever sentenced to or served a day in prison, is under indictment for any crime punishable by more than a year in prison, is a fugitive, is an unlawful user of any controlled substance, has been, adjudicated as a mental defective, has been committed to a mental institution, is an illegal alien, has a dishonorable discharge from the military, has renounced their U.S. citizenship, is the subject of a restraining order restraining the person from harassing, stalking, or threatening an intimate partner or the child of an intimate partner, or who has been convicted of a misdemeanor crime of domestic violence.