The sale and transfer of firearms, all firearms sold, traded, given or stolen need to be a counted for in a DOJ data base (or in such a data base in the State). No law abiding gun owner will continue to have a legal firearm; not only will the 4th Amendment protect law abiding US Citizens, no one who is law abiding will keep legal firearms until death do them apart.
Ghost guns are illegal and if any person who makes, owns, possess or is in their custody will be indicted for a felony with serious penalties - custody of more than one year and a day as well fines up to $10,000 - and they will lose the right to own, possess or have in their custody and control firearms for life. Having any firearm will become another serious felony and another time spent in a state or federal prison.
As to making an laws to prevent mass murder, which is a common event Homeland Security (H.S,) needs to survey the Internet and Social Media for people who write threats, or are so disaffected need to be investigated by local authorities immediately.
All Probation/Parole agencies, Social Service agencies, local and state LE Agencies and the courts need to notify H.S. with the terms and conditions of those released from custody, Civil or Criminal, who are a danger to themselves or others.