Sandy Hook Promise, a nonprofit formed in the wake of the shooting on 12-14, says some key warning signs have emerged in the investigation of the fatal school shooting in St Louis.  The missed warning signs included the shooter’s self-isolating behavior and a previous domestic disturbance call to his home where his mother found a gun.  The gunman was reportedly blocked from buying a gun after an FBI background check, but purchased the weapon through a private seller.  Sandy Hook Promise cofounder Mark Barden, whose son Daniel was killed on 12-14, says Missouri's lack of an extreme risk protection order laws also led to the gun violence.