Update: This document from The Smoking Gun was originally called to my attention by Wim Dankbaar on the forum at www.jfkmurdersolved.com
From there it was picked up by Cannonfire where Joseph Cannon has picked up on an interesting lead, which he plans to pursue further.
Joseph Cannon summarized the document:
This FBI memo from August of 1971 summarizes an interview with a lady named Lila Hurtado, who, in 1968, had worked for one William R. Huntington, an interior decorator "to the stars" who kept an office on Sunset Boulevard. (The text makes it clear that he was gay, a fact which may be relevant.) Huntington told her of a tape recording made by a friend of his, an attorney named Ronald Buck who owned or ran a club called The Factory...I did a search at NARA on the informant in the document, Lila Hurtado ,and came up with 32 hits, including a rather long document she wrote called "The Judas Movement" and a tape of Hurtado under hypnosis.
According to Hurtado, Buck had made a secret tape recording of several "wealthy individuals" hobnobbing with bigwigs from Washington. These worthies were "gloating" over the deaths of JFK and Martin Luther King, and discussed plans to deal similarly with Robert F. Kennedy, who was then running for the Democratic presidential nomination. Buck later played the tape for Huntington, who called Robert Kennedy. (How did he get the number? Probably via Peter Lawford, who was one of Huntington's clients.) RFK personally heard the tape while in California, and responded: "I can't do anything about that until I become President."