Oswald had only seconds to decide whether to take that early shot and the choice he made isn't going to necessarily be the one you would have made had you been in his situation. The only risk to taking that first shot is it would have alerted the protection detail and if they had reacted quicker than they did, Oswald might not have had a clear follow up shot. Again, Oswald could very well have made a different judgement call than you would have. He knew he had four rounds in his rifle and a limited time to fire them so he might very well have decided to get in as many shots as possible in the limited window of time available to him.
Again, Oswald could very well have made a different judgement call than you would have. Yes, and the same applies to your thinking.