One of the early conspiracy books, "Who Killed Kennedy?" (May 1964) by Thomas Buchanan, promoted the idea that the City of Dallas and Texas were behind the assassination. Oswald had been given a job in a "municipal" building (ie: the Texas School Depository Bldg, which is actually a private concern). A Texas oilman was behind the assassination. Officer Tippit (supposedly a right-wing member of the right-wing Dallas Police) fired from the Oswald window while a co-conspirator fired from the rail-bridge. Then Tippit was himself murdered to further frame young Lee. Buchanan based much of his "research" on newspaper articles that he had read while working in France.
Sylvia Meagher wrote one of the most influential books for CTs, called "Accessories After the Fact" in which she argued the Dallas Police were complicit in the assassination and alleged cover-up (though she didn't use the word alleged). Meagher was a NYC "Liberal" with a bias towards the South and conservatives. Penn Jones Jr. wrote of the "big league boys in Dallas".
Dallas, at the time, was largely ruled by the Dallas Citizens Council, a group of several hundred businessmen, most of whom were in banking and insurance. The City Council and Mayor were secondary. The Dallas Citizens Council should not be confused with the segregationist White Citizens Councils. The Dallas Citizens Council weighed the consequences of resisting integration of its schools and produced a film ("Dallas at the Crossroads" 1961) promoting integration, which went ahead in Dallas. The "shadowy" "ultra-conservative" Dallas Citizens Council (even if their measured decisions were mainly meant to ensure prosperity and keeping the races from each others' throats) became the basis for some conspiratorati that the city facilitated the assassination and much of the "cover-up".
The Shaw Trial suggested that the seeds of the assassination could have occurred in another city. Then came the King assassination in Memphis and the RFK assassination in Los Angeles, and it seemed rather silly to blame a city per se. It would be like saying nothing changed in NYC after the murder of Kitty Genovese, in Beantown after the Boston Strangler, and Chicago after Richard Speck. Today's JFK assassination "conspirators du jour" go way beyond the municipal level and the power of one oilman. It's almost quaint that the city was once singled out.