The Gemstone File is one of the first areas I looked into relating to the Kennedy assassination.
Here is a brief summary of what I found:
1. Most people have only seen The Skeleton Key to the Gemstone File which is a brief summary, approximately 23 pages of the actual Gemstone File which was consisted of about 350 pages of letters of the late Bruce Roberts which Stephanie Caruana saw in the files of the late Mae Brussell. There have been six books written about Gemstone and none of the authors of those books had ever seen the Roberts letters (Kenn Thomas had one page which he received from Martin Cannon--the author of an internet article titled Gemstone Exposed.
Martin Cannon has a copy of the whole set and so do I. One day soon I will post the whole thing.
2. These six books all say that the Skeleton Key was first published in Hustler in 1979. Not true--I located a version of the Key which was published in City of San Francisco
magazine in 1975. This version has a few interesting differences from other versions--for one thing it lists the Mossad as a participant in the JFK conspiracy. This magazine (edited by Warren Hinckle and published by Francis Ford Coppola, director of The Godfather
) also contains an account by a group called the DNA Research Collective of their meeting with Bruce Roberts. This group also put on a play about Jack Ruby called Sparky and Truth Detector
3. Bruce Roberts was somewhere between extremely eccentric and clinical. Nonetheless he may have had an actual source on the assassination. According to Stephanie Caruana (the author of the Skeleton Key) his brother Dayle was married to a woman Marina whose brother Antonio Iglesias had knowledge of the assassination. He was described as a CIA and Mafia connected anti-Castro Cuban. (Aren't they all?)
Further research indicates that he existed and that his full name was Antonio Iglesias Pons--a member of Brigade 2506 and described in one CIA document as a "former employee" of the CIA. This individual is also mentioned as being involved in the year 2000 plot to kill Castro which was headed by Luis Posada Carriles--recently in the news.
4. The Skeleton Key mentions "Project Star"--described as a top-secret study of the assassination conducted by Rand. Roberts had no inside source here--this study was mentioned in an article in Ramparts
by Anthony Russo (associated with Daniel Ellsberg in the Pentagon Papers case.) Penn Jones also picked up on this reference. This study did exist and was conducted by DARPA (actually known as ARPA at the time as I recall.) It was a study of Presidential Security. I have a list of the Project Star reports but not the reports themselves.
5. It was my Gemstone research by the way that indirectly led me to the now infamous McCone-Rowley memo. See http://mccone-rowley.blogspot.com
The source who provided that document to me, James L. Moore, has also claimed to be the real author of the Skeleton Key. I believe that he may have submitted the Skeleton Key to Hustler before they published it, but that they already had it from other sources.