Stop playing games.
Seeing the policeman actually fall down clearly indicates that the shooter would still be looking at the victim and most likely continuing to point the revolver at him, not knowing if his target had been rendered ineffective or not. This seeming fear & uncertainty is confirmed when ProbablyOswald then made sure by shooting the poor dumb cop in the head.
The not really Oswald at all would deliver a Coup d'Gras for a particular reason-
So the cop would not ever talk again... Why? Speculation. The cop was involved in a plot perhaps.
Maybe alive he would name names. Some one just merely trying to 'get away' wouldn't need to apply a capper. Needless. Save the ammo for another possible encounter. Chapman loses another round