The kill shot impacted the top of Browns skull and travelled downward relative to the position of the body. This is consistant with it having been taken at close range as the body was falling forward.
For your scenario to be true, the second shooter would have needed to have been a sniper with a rifle, I think. And probably firing a round that would have had an explosive impact on the skull. Like with JFK. Not consistant with the pictures of Brown’s body lying face down with an intact head and stream of blood running down from the front of it.