I would demand more than just physical evidence of the gun. First and foremost, I would demand x-rays and autopsy photos to be produced in full and call my own expert scientists in the field to examine it. All of that was hidden from public and most of it still is - if it hasn't been shredded. I would dispute different cartridge casings at the scene and make a statement that a premeditated assassin would know exactly what armor and lead he is using and select the rounds carefully - not a mismatch. If you like accuracy of Remington or Winchester, you stick with it!
I would put him on the stand.
I would also try to expose what ties he had already in the past with the CIA, possibly their special affairs staff (SAS). I am sure he knew already that he couldn't win when he was arrested in the theater. At best, he would have to incriminate the others that have made him into the lone assassin so he wouldn't hang alone. That was only defense! I don't believe that would have been hard to do. He already said he was a patsy and innocent. Given the opportunity (only 24 years old), he would have song like a songbird. Being a patsy is slightly different than being framed. It implies that someone else has knowledge besides you and was working with you. You were not acting alone!
First you need to understand his situation and concoct a plausible story and links no one wants to prove. A matter of national interest if there are ties. It was best just to remove him. He looked like a talker when he came in front of the camera!
Prior to the assassination setup, LHO might have even being coerced into believing he was some sort of double agent, working to gain foreign country access, to gain him spy status and work as a mole in a faraway land. (I advance this theory because he could have thought himself to be a Jason Bourne type figure and going deep undercover - he may have been mentally taxed and suffered from delusions of grandeur!)
He would defect to Russia, learn Russia, maybe defect to Cuba, learn Cuban - whatever they wanted him to do. If he thought he was deep undercover and his handlers were in on it, his links from SAS or CIA are unlinkable and won't be uncovered. That would be a situation suggesting redaction of sensitive sources, a matter of national security and conspiracy would ensue if you were allowed to go down that path. As a defense lawyer, that is best you could hope for operating against an unaccountable CIA or FBI organization that would be trying to hide its activities.
How did he manage to defect and then easily gain his passport back? Then, just 18 months later, he decided to go to Mexico City to try to gain a Visa to go to another Communist country Cuba? Those are serious questions. First Russia, get rid of passport, get it back, then go to Cuba to do what exactly? As a defense lawyer, I would play it to the hilt that he was innocently following a scheme laid out by his handlers and that he had no hope of escaping what they required of him in his duty as a great countryman and patriot. If he had ties, he would have to reveal his story as much as he felt safe to do and put huge amounts of pressure on the deep state. Great argument to use. Best he ends up dead, no loose ends and the story and history is written around and about him without his input!
I would also question what his purpose was to go to the theater and if he always carries a handgun. Make it clear, that if you were the killer of the POTUS you wouldn't just hang around! Since we know he owned a handgun, did he always carry a concealed weapon? Call independent witnesses in the theater to verify that he had a handgun when he was arrested and someone took it in as evidence. After leaving work early, ask if he did go back to his house, change clothes and then walk back to a theater. "Why did you go to theater and what was your purpose to change clothes?" "How many handguns do you have in your house?" Is or are they automatics? Do you own any others such as .22 revolver? He surely must have been smart enough to know that early on he was a suspect or involved - otherwise you wouldn't arm yourself, shoot a policeman and then disappear into a theater after walking from your house. Did someone tell him to go there and if so who did and what was motive? Did he pay or sneak in? Good questions someone to determine a second angle to the story.
Why carry a handgun to the theater? Is that common practice in the day - especially if you claim you are innocent and a patsy. Ask him to retrace his steps on the day. Confirm his presence by asking where he was when the shooting take place? Did he have any witnesses that can verify it? Did he go home? Did he walk? Did anyone give him a ride? Important questions to see if he can answer or just avoid answering and take the fifth.
I would also question him on his mental cognizance? I would ask if he was trusted to have any security clearance while in the military? At what level was he granted clearance? Ask him if he remembers how many times he was court-martialed and discuss? Open up his military record and examine it.
A pre-planned self prepared assassination plan takes time and effort and is not happenstance when CIA and FBI have watched him for weeks/months and have a file on him. Was he aware of the motorcade route and when did he first learn the President was coming past the TSBD where he was working? Did he own a handgun or a rifle? Ask him to describe the rifle or admit/deny ownership of the Carcano? He may well deny owning any gun. Or if upon examining of the evidence, presented against him, ask for an explanation of using an alias signature in the purchase. Have him explain in his own words why he thinks he was a patsy?
I also would question if he remembers what he ate at lunch that day or where he ate it? Any witnesses? Did he eating a chicken sandwich? Did he bring a lunch from home and did he pack it himself? Confirm which floors he worked on and if he was on the floor where the shots purportedly came from that day.
I would also use witnesses that said the shots were fired in quick succession and also witnesses that said it came from the fence and present that. If everyone ran to the grassy knoll, I would present as many witnesses that backed that statement up as possible of where they thought the shots came from. That is an effective case to put forward as it suggests no one knows exactly where shots came from and he is the patsy.
It is also worth explaining the physical limitations of a bolt action rifle mounted with a scope and having to reload between shots. It is also necessary to point out that at age 17, he was considered a marine sharpshooter (score 212) and he was considered only a marksman 2 1/2 years later in 1959 (score 191). Uncertainty should be drawn whether or not that markmanship included moving targets or a stationary one. I would also ask if he attended shooting ranges regularly to keep up his marksmanship and how many times he did it in the last 4 years. He should also be asked if he was an avid hunter and if he had a gun when he had sighted in and used it. Did you maintain practice in Russia and in the last 18 months that you came back from there? Are they any witnesses that saw you practice with the Carcano? We can't expect to believe that someone can hit a target at 10 mph at least twice without carefully setting scope and gun - a topnotch marksman without practice! I would also take the gun in question and shoot some rounds at a target and see if it is capable of firing accurate rounds at a bullseye. If it can't repeat well or off target, how can this be the weapon? That is a logical argument to launch to defend yourself and needs to be proved.
I would also bring an old injury out and discuss which hand he writes with? Also which shoulder he shoots from, left or right. He was court-martialed 3 times, once for shooting himself in the elbow with a .22 while on duty. Which elbow was it and did he suffer bone injury or did the bullet pass through without incident. Is it stiff? That may been able to be used to support a slow response or incapacity if injured of firing rapidly. (That is same sort of argument used by OJ Simpson when he couldn't get the bloody glove to fit his hand in the court when presented with it. It worked for him!)
Of course as a lawyer, you would never have been allowed access to FBI Director Hoover's memo comment. If you would have, it would have been bitter/sweet evidence to use to cast serious doubt of the allegations against your client!
https://www.newsweek.com/jfk-assassination-files-hoover-wanted-public-convinced-oswald-was-real-694324"The thing I am concerned about, and so is Mr. Katzenbach, is having something issued so we can convince the public that Oswald is the real assassin," Hoover said in the 1963 memo.
I think I have enough for a book, anyone want to buy it!!!!!!