Debunk This: JFK's driver killed him with dart gun

My brother at dinner mentioned that he believed that "something weird" was evident in the JFK assassination video, and at a certain point it looks like the driver pulls out a pistol like object and leans in to fire a fatal shot (CW the jfk assassination video 22 seconds in a man with a suit pivots towards JFK), While no bullet hole matches the potential pistol shot, he claims that possibly it was a gas powered dart gun loaded with tetrodotoxin. Possible evidence for this includes JFK's brain never being properly given a toxicology report, and his brain matter being missing. Possible motivations including killing JFK because of his opposition to the Vietnam war.