Most witnesses in the Garrison investigation came forward after the Warren Commission and the FBI investigation. Perry Russo, Charles Spiesel, and the Clinton and Jackson witnesses hadn't said a word for years before then.
Stephen Roy, in his unpublished biography of David Ferrie, Perfect Villain: David Ferrie and the JFK Mystery, wrote:
"The 1963 Ferrie investigation was as notable for what did emerge as for what did not emerge in 1963. In terms of later allegations specifically connecting Ferrie to an assassination conspiracy, Perry Raymond Russo and Charles I. Spiesel did not come forward. In terms of later allegations of a 1963 relationship between Ferrie and Oswald, Delphine Points Roberts, David Frankin Lewis Jr., William George Gaudet, Thomas Edward Beckham, Raymond Broshears, Ronald LeVore Lewis, Judyth Vary Baker, Van Burns, Joseph Samuel Newbrough and the Clinton/Jackson witnesses did not come forward. The name Clay Shaw did not emerge in 1963, so a long list of people alleging a relationship between Ferrie and Shaw did not come forward. In short, all that emerged in 1963 were Jack S. Martin and a few people alleging that Oswald and Ferrie may have served in the Civil Air Patrol at the same time, eight years before the assassination."
So, let's have a look at what these people said about not coming forward.
Perry Russo was asked in the preliminary hearing why he didn't contact the FBI or the Warren Commission after overhearing a conversation about killing JFK.
At the Clay Shaw trial, Russo was asked why he didn't immediately report the threat on Kennedy's life.
None of the Clinton witnesses came forward either. Here is a short snippet from Lee McGehee's testimony:
Here is John Manchester's testimony from the Shaw trial.
Corey Collins was also asked about why he hadn't come forward.
And, here is William Dunn - he actually had them laughing in court.
Reeves Morgan was the one witness who claimed to have called the FBI after recognizing Oswald on television:
But, did Reeves actually call the FBI?
Andrew Sciambra wasn't taking Morgan at his word. He sent a letter to the FBI asking for further information:
This prompted the FBI to look into the matter:
Nonetheless, a letter from the DOJ was sent to Sciambra:
Sciambra then wrote to J. Edgar Hoover:
And, that prompted yet another memo:
Of course, Clay Shaw's defense team was NOT informed that not only did the FBI had no record of any communication from Reeves Morgan regarding Lee Harvey Oswald, but that they had so informed Garrison's office.