I found this telling.

https://books.google.com/ngrams/graph?content=conspiracy+the...

Thanks for the correction. I think it would have been better for me to say that counter-intelligence operations in the country have long intentionally colored inconvenient facts as wild conjecture, regardless of their historical foundation.

that's such a silly conclusion though, and really a perfect AP piece. It discredits people while saying nothing.

It doesn't matter if the phrase existed before hand, it very obviously blew-up during the JFK event.[0]

It could entirely well be that the DoD didn't invent the phrase, but it's pretty obvious that it very quickly became a part of the public verbage during heavy interest in the JFK event -- that trend could have easily been the indicator of work towards the discrediting of both the term and those that had too much curiosity towards things they shouldn't question.

[0]: https://books.google.com/ngrams/graph?content=conspiracy+the...