I heard back from Ed Chiarini. I had asked him about the source of the footage he used in his video, in which we can see the action very clearly, including the moment of impact, unlike the highly evasive NBC footage. Ed said that it came from Dallas County District Attorney's Office. He said he got it directly from them.
But, what I still want to know is who took it? Who was the cameraman? Who was he working for at the time? And where was he located in the garage? Obviously, these answers will be known soon.