“So plausible that an honest, dispassionate observer could easily come to believe it to be the most likely way it happened.”
Certainly plausible, but he could have turned because he heard someone behind him yelling commands, he could have reached for his side because he was shot or to grab his weapon, he could have pointed because he recognized someone or because that person shot at him. There are many plausible explanations.
IIRC, he was left handed. Reaching to his left side with his right hand would not have produced a weapon.