I agree that this interpretation is very possible.
If there is no proof of prior coordination with the McMichaels to forcibly confront a specific "trespasser", I think the case for murder charges against WRB is weak. There seems to be a ready defense of:
- My unsophisticated client knew that GM was a retired police officer and heard that a current police officer had "redeputized" him.
- My client made a bad judgement in good faith by presuming that GM had lawful arrest authority and was making a lawful arrest. He then impulsively assisted GM to make the arrest.
- My client was not armed. He immediately ended his assistance when things did not look right.
- My client did not kill anybody, and had absolutely no knowledge that GM was predisposed to unlawfully confront the victim. My client did not encourage the use of force either directly or indirectly.
- In fact, my uhmm.... "shocked and appalled" client immediately turned his video over to the police for review- again, in good faith ( the fact that WRB was not appalled cant be proven).
I understand what you're saying, that you believe the case against WRB would be stronger if prior coordination with the MMs could be proven.
Leaving aside whether or not the State has any such evidence that can be produced at trial, what was argued at the preliminary hearing gives clues about what WRB's defense might be.
To convict WRB of felony murder, what the State must first prove, beyond a reasonable doubt, is that WRB is guilty of the felony of falsely imprisoning AA.
GA's legal definition of false imprisonment: it's when one "arrests, confines, or detains (a person) without legal authority."
The question at trial, then, is whether or not the actions WRB took that day to "block" AA (his own words) meet the legal definition of false imprisonment.
Several of the (implicit) arguments made during the preliminary hearing that WRB's actions didn't meet the legal standard for false imprisonment are similar to yours.
Primary argument made at hearing: That there was *not* any coordination between the MMs and WRB. WRB saw a pursuit and joined in, but did *not* coordinate with the MMs about where to try to confront AA again off of Burford (after the MMs left Buford and circled around on Zellwood).
It's pretty clear what WRB's attorney would also like to argue at trial. And that is, the nature of (and perhaps reason for) WRB's pursuit of AA changed after his initial attempts to block AA in, when AA supposedly "attacked" WRB's truck and tried to force open the driver door, perhaps (most egregious accusation) in an attempt to carjack WRB's truck.
Bottom line is that if the jury believes what WRB did that day constituted false imprisonment, whatever his intent or motivations, then WRB is also guilty of felony murder, because AA was killed during the commission of the felony of false imprisonment.
The fact that this young man lay there dying after running and then fighting for his life for several minutes with nary an attempt at offering aid, never any urgent calls for an ambulance, nothing but the voices of the men responsible and law enforcement officers as they vilified the dying young man within his earshot. Just so upsetting. several minutes of terror, then excruciating pain, then to lay there with others, including LOEs, walking around you and discussing you as if you were less than a dog. 
