I watched the interview with the former officer. I took away that he believes there were some suspicious actions/ statements by other officers at the time, but he had no first hand knowledge of the murders. The license on the dash certainly lends some credence to the police/ police impersonator theory, but I'm not ready to put my eggs in that basket just yet.
According to Allen Forrest's (Bookie's) video, the girls asked for directions to Midland City so obviously they were headed in the direction of Midland City/ Ozark. JB sister said the person they were speaking to on the payphone from Headland was a friend and that has been checked out. Whoever they spoke to was the first link in the chain that set them on a path to Ozark so I would certainly take a look at the person to whom JB spoke and anyone who was with or this person that night.
Also, in her interview JB's sister says that JB told Bookie they had taken a wrong turn and ran into 2 white dudes with shirts off that started following them; however, in his short interview Mr. Forrest said he did not remember telling anyone that. That doesn't seem to be a detail that one would forget. Could it have been another witness that said that, Ms. Merritt perhaps? If so and they were being followed later in the night, that certainly could help focus the investigation. Were there any witnesses that place the girls at the informal party in Ozark? If not, how did this theory emerge?