The key to this entire incident may lie with this knucklehead’s actions.
If the officer thought that he was facing two assailants, he was justified in firing until Brown was down.
Good point...seems to me, especially with the revelation from Wilson’s friend (corroborated by an eyewitness whose voice was unknowingly recorded describing the shooting immediately afterward at the scene) that Brown doubled-back and charged at Wilson, even without Johnson, it was a justified use of deadly force all the way, however your point bolsters the argument.