I have told this story many times because it is one of the most convincing pieces of evidence I've ever read on the extent of the JFK murder conspiracy. It comes from Jerry Bruno's 1971 book "Advance Man" written with Jeff Greenfield.
The Dallas trip was intended to help heal the Democratic party rift between the conservative wing, led by LBJ's protege and "son I never had," Texas governor John Connally, and the liberal wing led by Senator Ralph Yarborough.
Bruno recounts the long standing dispute over where JFK would give his Dallas speech. Connally, personally overseeing the trip for Texas, had long insisted upon the Trade Mart, along the Stemons freeway, reached by turning onto Elm to get to the onramp, where the audience would be primarily business leaders. JFK's team, under Yarborough's guidance, insisted upon the Women's Hall, a union hall which held a much larger audience, reached by continuing directly down Main Street. This dispute had been resolved at the WH, some say by JFK himself, before Bruno left for Dallas to arrange the trip. Bruno was the WH man on the scene and had to approve all arrangements for the visit.
On the 19th or 20th, Connally sent for Bruno, asking him to come to his office in the governor's mansion. Bruno arrived and was ushered in. Connally again made his pitch, citing some new pretense. Bruno refused to change the venue, noting the WH's insistence. Bruno describes how he sat in the chair in front of the governor's desk as Connally tells him he will personally clear the Trade Mart venue with the White House then and there. He picked up the phone, dialed, and had an apparently detailed conversation with somebody at the other end. He even waited as the person "checks" with some higher authority. After a few minutes, the conversation continued. Connally thanked the person, hung up, and announced to Bruno that the deal was done, and JFK now approved of the Trade Mart site. Thus the route is now to be changed, taking the motorcade directly under the Texas School Book Depository building, around the hairpin turn, and down Elm at 12 mph instead of down Main, another hundred yards away from the TSBD, at the mandatory minimum Presidential motorcade speed of 35 mph.
After the assassination, Bruno was intrigued about who gave the authority to change the route. He could find nobody at the WH who took Connally's call or approved the change. Finally he had the WH phone records checked and found there was no evidence of any such call ever being received.
Bruno was called to testify before the HSCA in 1978 at the insistence of David Lifton, a JFK researcher. His testimony was held in secret, was sealed, and currently remains locked up, I believe, until 2028, according to Lifton's 1996 testimony before the Assassination Records and Review Board at:
http://mcadams.posc.mu.edu/arrb/index38.htm .
In a just world, Bruno's first person testimony would constitute indictable evidence against Connally, a point man, imo, in the conspiracy.