Annual universal background checks that require psych profiles and are conducted by a judge in a courtroom
A federal firearms dealer has a profit motive to look the other way
Close the gun show loop hole
Registration
Waiting periods
Heavy taxes on ammo
Banning semiautomatic weapons
Jail for anyone who has a weapon stolen from them or loses them and fails to report the incident
.
For starters
.
And they apply, in varying degrees, to all of the other tragedies as well
.
Now's your turn to try to tear all of those down.
But the only solution that will fit your immediate need for 'this tragedy' is a magic wand.