La Cosa Nostra, Castro & maybe even FBI.
Possibly one or more together. (Especially Mob & Castro).
All had more than 1 motive.
I've believed all along that the FBI killed Marilyn Monroe.
(Who was banging JFK, and knew too much. Their adultery brought
shame into the "Royal Family" of the US).
It was well known that J. Edgar Hoover and the Kennedy's hated each other.
I wouldn't be shocked if they were proven to be involved.
Mob wanted JFK and (eventually) RFK taken out (after RFK became Attorney General,
and started going after the mob).
And what was Oswald's motive again?
Ruby was a small time hood, with ties to the mob.
Had access to (in a Police Station) and killed Oswald to shut him up.
Oswald was a sucker. Used; a patsy, a scapegoat, a nobody.
Always intrigued by the many different theories.
Hope someday we'll know what really happened.

Oz