Nagell himself claimed to be a double agent, and that he was assigned by Moscow to interdict LHO, who had been trained to assassinate JFK.
Unfortunately, Nagell appeared troubled. Also, the provenance of whatever was in his lawyer's office papers is unverified, including the dubious Hidell ID card, which was likely fabricated after 11/22.
That there was interaction between LHO and G2 and KGB all along the line in the second half of 1963 is indisputable. That Castro threatened the Kennedy brothers in September '63 with a revenge assassination attempt is matter of historical record.
The US Ambassador to Mexico, Thomas Mann, and the State Department staffer Charles Thomas, both thought there was a lot to the Cuba-LHO connection, and they were both shut down.
In some circles, the LHO as G2-KGB asset version of the JFKA is heresy. I am open minded.