Hopeless. The obvious point is that an otherwise legal, not uncommon action can - when examined within the totality of circumstances in a case - become probative of guilt. Even if standing alone it would not. Buying a life insurance policy just prior to a mysterious death is the classic example. Oswald's decision to leave his wedding ring at home for the first and only time of his marriage according to Marina along with an unusually large amount of money (during an unexpected visit to the location where he stored the rifle) on the day when other evidence links him to the assassination demonstrates foreknowledge of his potential arrest or death that day. He wants to ensure that his wife has his wedding ring and as much money as he can provide his family before he is separated from them. Now what was so dangerous that day that might lead Oswald to believe he might never be coming home? Find someone in your community with a functioning brain to help at this point if you need further assistance.
Marina said that she was shocked to find the $170 that he left her. It must have been, she said, all of his money.
She said his usual routine would be to leave her a few dollars - repeat a few dollars - on Monday, when he would return to his rooming house, to buy things for the children. He told her, he said, he would see her again Saturday and Sunday but because he stayed on Thursday would not stay overnight on Friday.
So he could, as was the usual routine, leave her a few dollars on Monday. But he didn't; he left her money on Friday. And far more than, Marina said, he usually left her.
The "lots of other men do things like this" response is given either because the person is quite illogical in his thinking (hint: Oswald was not like "lots of other men", e.g., "lots of other men" who left their wedding rings and nearly all of their move that morning didn't work in the building where someone shot at the president as he rode by, et cetera, et cetera) or because he is trying desperately to absolve Lee Oswald in the act of shooting the president.
Or perhaps both.