This actually comes from the comments section:

In 1913 Congress passed The Federal Reserve Act which gave the right to create currency to the private bankers. They selected the operating name The Federal Reserve Corporation. Despite all the name implies, it is a private organization benefiting from interest charged to the Nation by lending their privately created Reserve Notes to the country. As the debt spirals skyward the revenue to the banks soars as well.

In 1963 President Kennedy signed an executive order returning the banking operations to the country. $4 billion in "United States Notes" were printed to replace the private notes with a national currency. As article 1 of the Constitution states, Congress would regain the power to coin and regulate money and we would be a debt free nation.

President Kennedy's assasination followed and the new currency was destroyed. The banks remained in the hands of the members of the Russell Trust Corporation.

Speculation? Certainly. (A couple of other commenters who replied stated that they could verify the part about the executive order to issue U.S. notes, though I would need to do my own research before I believed it as a certainty.) But it would make plausible sense. If JFK was truly working to undermine the most closely guarded secret used by those who pull the strings (how currency/debt is generated, and by whom), then of course they would want to be rid of him! This also would be the same bunch tried and failed to mount a military coup against FDR (and would have succeeded had it not been for General Smedley Butler's sudden bout of conscience).