Even if Oswald's shooting skill are in doubt, the fact that he MIGHT not have been able to does not mean he COULD not have. All of us at times do things we might not ordinary be able to do, or repeat with consistency. I can give you a couple of examples in my own life. The last time I went golfing, which I think was the third time in my life, I went with two buddies. I was the last two tee off. My friends each sent mediocre shots down the fairway, slicing or hooking to the side. I addressed the ball, pulled back the club, and swung through. The ball rose, straight and long, bounding down the center of the fairway. It was the only such tee shot I made all day. It might have been the only one if I tried one hundred times, and it was the first one!
Another time, many years before, I went to an Angels game. My friends were bigger baseball fans than I, and I did not even bring a glove. They wanted to get closer to the field for batting practice to try and shag some fly balls hit into the stands. Suddenly one rose toward our location and landed on the grass. It obviously was going to bounce into the stands and everyone went for it. I just leaned, and as the base landed in my palm I close my fingers and caught it bare handed, in my left hand, and I'm right handed. How many times do you think, if we wanted to, that the guy pitching the ball, and the batter, and myself could duplicate that? How many times would it take? But it did happen, and just the same Oswald may have exceeded his normal ability just that one time. it is not impossible, and there is no evidence to that anyone else did it.