The Marrs lecture video is just a short visual summary of his best selling book Crossfire. I admit I'm not an expert on guns, never even fired one. This was a typo - meant AR. In the Smoking Gun video referred to as a "machine gun" by witnesses because they didn't know either what the agent in the car behind JFK was holding, only what it looked like. It's in the one photo- referring to whatever gun that was. If you think that the agent can accidentally shoot JFK in the head, then I guess anything is possible. The main problem I see from the The Smoking Gun video, is while the investigator bases his assessment by the data presented, unfortunately we have ample evidence that much of (or nearly all) the evidence (including the shells found/picked up never seen again/Oswald's alleged gun used, holding in photo and fingerprints on/the autopsy), have been all either been tampered with, destroyed or planted by the CIA to fit their narrative. So the data is compromised which we base the investigation on, leading to some erroneous theories based on faulty data. Otherwise, the investigator did all he could with what he was given, and that is to be commendable and understandable.