ABC last week revealed that it had bought the rights of Mr Hersh's book, The Dark Side of Camelot, which it had hoped to turn into a documentary. However, the network had unearthed a problem which meant the project either would have to be recast or simply shelved altogether.
The hitch pertained to the most tantalising claim contained in the book - that letters exchanged between JFK and Marilyn Monroe in 1960 revealed that the former president had proposed paying off Ms Monroe in exchange for her agreeing to keep quiet about an affair between them. Specifically, he would hand over $600,000 for a trust fund for Ms Monroe's mother.
Mr Hersh had the relevant letters. But ABC had spotted problems with them that had eluded the author. One, dated 1961, had a zip code, when the codes were not introduced until 1962. Meanwhile, experts concluded that the make of typewriter used was not manufactured until 1970.
Now another network, NBC, has revealed that it had previously bought the rights to the Hersh book with a view to making a film and that it too had been forced to abandon the project. The implication is that NBC discovered the same faults in the book that ABC did months later and that Hersh none the less re-sold the rights to ABC in full knowledge of them. Hersh and a partner received $1m from NBC. The subsequent deal with ABC has been put at $2m.
NBC's President of Entertainment, Warren Littlefield told the New York Times: "In our investigation of the documents, serious questions have been raised that we cannot answer".