Why wait? When the government investigates itself, the government always wins. We know what the police will rule - the cop is NEVER at fault. The eyewitness is confused because she saw her friend handcuffed and then suddenly he wasn't anymore. Pretty obvious reason for that. The cop knew that shooting a cuffed arrestee could (and should) escalate into a Murder 1 trial, so he removed the cuffs so he could say the guy got the drop on him.

But, it doesn't matter, because the super investigator is going to find that the shooting was completely justified. Cops could mow churchgoers down on the sidewalk and that's what the investigator would conclude.