Congratulations! you are the first person on the several threads I have looked at who has grasped that simple truth.
Way too many self proclaimed ‘gun experts’ have been saying that it was an amateur thug with a malfunctioning gun. I say it was a pro who knew well in advance that he would have to rack the slide every time, and had practiced it.
While the shooter may have shot people before thereby considered a ‘pro’, I doubt his experience. A real pro would have used a revolver so no spent shell casings could be found at the scene. Empty shell casings sometimes have fingerprints on them from preparing the ammo and/or from the loading of the gun.