Fully automatic weapons (and soon, semi-automatic weapons) are illegal, therefore that is impossible.
Full auto are not illegal. With a $200 federsal stamp you can own and carry concealed as full auto weapon. Same with sound suppressors on weapons. BTW, a full select fire Thompson will set you back around 15 to 20 grand, but can be owned legally.
And further more, shirley the perps had their stamps up to date and with them when carrying the full auto weapons don’tchaknow. Failure to do so could be hugh and series.