Why do you think Brown and Johnson were not in “immediate flight”?
They were stopped by Officer Wilson literally less than ten minutes after the robbery, they were carrying the stolen goods at the time he stopped them, and it appears likely they had not stopped anywhere in the meantime but had proceeded on foot directly from the scene of the robbery to where Officer Wilson stopped them.
In my jurisdiction we could not charge Johnson with Brown’s death because our felony murder rule is interpreted so as not to include the death of a co-felon (but we can charge a felon with the death of a bystander or a cop).
Even in jurisdictions that allow a felon to be charged with the death of a co-felon sometimes there is an exception in the case of a co-felon killed by a cop. I have no idea how the rule is interpreted in Missouri.
I just don’t think that walking leisurely down the middle of the street would be held as “immediate flight” from a felony. Like I said before, it’s debatable that the theft of the cigars was even a felony robbery in the first place. The Missouri Statutes only state that “a death of another person” can qualify as felony murder. However, I don’t know off the top of my head whether or not that includes co-felons. I’m also replying from a restaurant on my phone, so I don’t have any of my legal research stuff at my disposal.