one doesn't need to go into whether or not he acted alone to know that something smelled about that guy. But with all that you mentioned about Oswald, that he got back into the country just by asking, with his wife, with money given to him by the US government to fly here, and we're supposed to believe that J Edgar Hoover's FBI wasn't watching every move he made?
Never underestimate the power of stupidity. It explains a lot more than conspiracy. Our law enforcement agencies were warned by Russian intelligence that the Boston bombers were heavily involved in Muslim terrorist groups in Chechnya. After they committed the terrorist act, police agencies locked down Boston and a few suburbs for a day to try to catch the surviving brother. After ending the lockdown, a local resident found him without police assistance. Despite all the blather about “Boston Strong”, the whole incident highlights law enforcement incompetence. The FBI and State Department were clearly as incompetent a half century ago.