Say what you will about LBJ, he knew how the world worked.
Not too long after JFK was killed, he had a meeting with the head of the SS and made it clear he was considering have the FBI and Hoover take over presidential protection, and that he and his entire operation would be doing counterfeiting stuff only.
The SS guy got the message.
Rowley was part of the plot to take JFK out in Dealey Plaza. He was always a LBJ yes man.