What about the in the concert crowd telling everyone they were going to die that night, hours before the shooting?
Perhaps the warning woman knew a maid to the Sauds who overheard them discussing their discovery of the asassination plot. Blowing up the fuel tanks for Air Janet may have killed all 20K by concussive blast alone.
Air Janet right there lends credence to Salman Jr. being there with a large entourage.