PBS archives bring us these few important words as we consider the far-flung interests and involvements of this most corrupt man.
"Joseph Kennedy was designated one of two Special Service contacts to the FBI's Boston office in 1943. In this capacity he reported things he thought the FBI might want to know, sometimes corresponding directly with J. Edgar Hoover." (6)
You can be certain that Hoover had the 'goods' on Old Joe and that this tyrant used him; but the question is which tyrant used the other one the most.