As a history nerd and hater of conspiracy theories, here is the first of five reasons Lee Harvey Oswald and Oswald alone killed JFK.
Oswald Acted Guilty
Oswald displayed clear consciousness of guilt. Of the many employees at the Texas School Book Depository, only Oswald failed to show up at the roll call after the murder. Of the hundreds of thousands of people in DFW, Oswald is the only person to shoot and kill a policeman moments after the murder. These are the clear actions of a guilty person.