I recall there was a Congressional investigation into the JFK assassination which (if I remember correctly) did not agree with the findings of the Warren Commission, but I don't remember if they did come up with their own theory of who was behind the assassination.
The CIA and the FBI play a prominent role in the book.
It is one of the best on the JFK assassination in my view—and I have read a _lot_ of them.
For info on that congressional investigation the best source is:
https://www.amazon.com/Last-Investigation-Gaeton-Fonzi/dp/151071393X
More detail on the CIA role can be found here:
https://www.amazon.com/Bond-Secrecy-Watergate-Conspirator-Howard/dp/1936296837/
In the last book E. Howard Hunt explains that he was in charge of CIA logistics for the JFK assassination. The Western Hemisphere division staff, agents, and contacts used standard operating procedure for the hit.
LBJ and J Edgar Hoover were in charge of the cover-up after the fact, with an assist from Operation Mockingbird agents in the mass media.