It does not matter, because most mass murderers have not broken any laws that could be enforced.
There is a speedy judicial review. But where red flags are needed there isn't time for full legal representation. To compensate for that, the actions taken through the red flag laws are temporary - pending a full hearing with full legal representation. If at the end of that hearing the person is found not to be a danger, his guns are returned. All due process is limited only to the extent necessary to provide immediate protection. Obviously that would not be the case if the accused retained all his rights to a gun while waiting for the hearing because if the danger was imminent, it would be too late. There are various forms of red flag laws already implemented in some communities. You can research them and see for yourself if they provide a reasonable balance between due process rights and the prevention of imminent harm.