Shotguns are illegal on Long Island? According to the NRA/ILA site(PDF), no permit is required for long guns in New York state, nor are they registered nor do they require a permit/license to carry. New York City, yes, but not New York State. Only handguns require all of the above in NY state. Do the various jurisdictions on Long Island all follow NY City practice?
He’s facing firearms charges, and so it may well be that the charges pertain to the revolver that he used.