https://www.washingtonpost.com/local/obituaries/cynthia-thomas-state-department-widow-who-won-presidential-apology-dies-at-82/2019/03/20/4bd2aaf2-4938-11e9-93d0-64dbcf38ba41_story.html
Philip Shenon focuses major parts of his book on the WC, "A Cruel and Shocking Act", on Charles Thomas' concerns that the government didn't fully look into allegations that Oswald was seen with Cuban officials when he went to Mexico City. Thomas was convinced that Oswald did indeed go there, that Oswald wasn't impersonated, but didn't think that what Oswald did there was looked into completely. But Thomas admitted that even if the reports were true, e.g, the so-called "Twist Party" where Oswald was allegedly seen with Cuban officials, it didn't indicate there was a conspiracy.
As he (Thomas) said in a memo in 1969 to then Secretary of State William Rogers, "Even if all of the allegations in the attached memo are true, they would not, in themselves, prove there was a conspiracy to assassinate President Kennedy." But he said that if the allegations were revealed to the public that "those who have tried to discredit the Warren Commission would have a field day in speculating about their implications."
For what it's worth, I think Oswald
did attend that party - Silvia Duran lied about it - and probably did meet with either Cuban officials or pro-Cuban people who may have helped fuel his anti-JFK views regarding Cuba. But connecting those conversations with the events in Dallas two months later is a reach.