In his 2009 article on evidence that Cuban intelligence had foreknowledge of the assassination and that Castro approved/allowed the hit on JFK, Gus Russo claims that while Oswald was at the Cuban Embassy in Mexico City, he wept and proclaimed that he would prove his revolutionary loyalty by killing "that bastard, Kennedy":
At the Cuban Embassy in Mexico City, Oswald pulled a gun, wept, and claimed that he would prove his revolutionary loyalty by killing "that bastard, Kennedy." ("Did Castro Okay the Kennedy Assassination?", American Heritage, winter 2009, https://www.americanheritage.com/did-castro-okay-kennedy-assassination)This was the basic fable that was energetically pushed by elements of the Intelligence Community and the news media soon after the assassination, i.e., that Oswald the devout Marxist killed JFK in the service of or in support of the Soviet Union and Cuba. This tale is still peddled by some lone-gunman theorists to this day.
Yet, this tale makes it all the more puzzling that Oswald did not do what other ideologically motivated presidential assassins have done, namely, proudly take credit for his deed and justify his deed as a worthy act done in support of a noble cause and/or done as a necessary act to combat evil.
Oswald did the exact opposite. He adamantly insisted he was innocent. He fiercely denied shooting JFK and/or Tippit. He said the evidence against him was fraudulent. He even said he was a patsy.