Rarely does a month pass that I read an obituary from an eyewitness to JFK's assassination or somebody peripherally involved in the aftermath.
Call if one of the demented benefits of living in Dallas.
Within the past few months, I've read obits from nurses who were on staff at Parkland when Kennedy or Oswald were brought in or policemen at the station when Oswald was brought in; a few days ago, the pilot who flew Air Force One back to D.C. passed away.
Carlos Marcello's favorite phrase was "Three can keep a secret if two are dead."
Granted, most of the figures who have lived this long are historical footnotes. They are not secret holders, but observers to those who were. The stories they could tell would not necessarily lend a whole lot of credibility to any particular conspiracy theory; their first hand information would probably not solve this 43 year old riddle -- that evidence was laid to rest before the eternal flame was lit.
However, the historical anecdotes are important nonetheless -- even if to provide a backdrop for the prima facie evidence or to bridge the gap between more damning information already part of the record.