Executive Order 11110 was issued by U.S. President John F. Kennedy on June 4, 1963

The #JFKFiles shed light on Jim Marrs' theories (per wikipedia) 

"Jim Marrs, in his book Crossfire, presented the theory that Kennedy was trying to rein in the power of the Federal Reserve, and that forces opposed to such action might have played some part in Kennedy's assassination.   Marrs alleges that the issuance of Executive Order 11110 was an effort by Kennedy to transfer power from the Federal Reserve to the United States Department of the Treasury by replacing Federal Reserve Notes with silver certificates.[24] Author Richard Belzer named the responsible parties in this theory as American "billionaires, power brokers, and bankers ... working in tandem with the CIA and other sympathetic agents of the government."
#JFKFiles