Well, we know the part about JFK being killed is not fiction.
Not familiar with those books but if they suggest both Castro and The CIA had reason to kill Kennedy I think either scenario is plausible.
Although I lean towards Castro.
'Course, Mafia boss Sam Giancana (sp?) probably wasn't too pleased that JFK was bedding his girlfriend.
I fully believe the evidence overwhelming supports the Mafia connection, although not over a girlfriend. Even back then, women weren't that important to the mob.
Old Joe Kennedy had gotten in bed with the Mafia to stuff the ballot boxes in Chicago and distribute cash through West Virginia. The payoff was to be the Kennedy administration laying off the mob.
Well it all worked out. The ‘extra’ votes in Chicago carried the day, and Kennedy won the electoral vote. Of course as soon as he was elected, he appointed his brother Attorney General, who immediately announced he was focusing on the mob.
This was the ‘old’ mob, the so called ‘men of honor’ guys who believed no transgression was to be left unpunished. Old Joe by then had suffered a stroke, so he wouldn't have known if he was alive or dead anyway. But there is some very incriminating tape the FBI recorded of Mafia bosses. One of their discussions includes, “if you can't hurt the guy anymore, you take away what he wanted.” Something like five months later JFK was dead.
Or that after stealing the election for him he appointed his brother AG and his brother's highest priority was to take down the mafia.