Obviously I know as much as anyone (nothing), but I would guess as soon as they (the would-be assassins) realized they had entered a trap they needed to create a distraction from their original intent. Firing onto a crowd was probably already planned out as their contingency plan. The master-minds likely chose that day to attempt the assassination because of the scheduled concert. The ones firing onto the crowd (Maybe Paddock?) were likely told to do so if things went sour to divert police resources to the wrong location (not the Mandalay Bay) to give them enough time to flee. Then before they could flee a clean up crew came through and tied up the loose ends. I suspect one day soon the world will know the truth.