IANAL, but for the sake of discussion.
What state is this in? Who authorized this agreement? Does he have it in writing? If it was next of kin who said "go to town on demo and keep anything you like" in writing, I suppose that would make your friend the legatee. What happens next depends on geographic location, but I suppose he would be the legal owner at that point. If this were MA, maybe (not 100% sure) MGL Chapter 140, Section 129C would kick in. Specifically:
(n) The transfer of a firearm, rifle or shotgun upon the death of an owner to his heir or legatee shall be subject to the provisions of this section, provided that said heir or legatee shall within one hundred and eighty days of such transfer, obtain a firearm identification card or a license to carry firearms if not otherwise an exempt person who is qualified to receive such or apply to the licensing authority for such further limited period as may be necessary for the disposition of such firearm, rifle or shotgun;