I have been re-reading this bizarre and fascinating case and still can't make sense out of all the pieces of the puzzle. There were so many links between Mary and Diane that it seems against all the odds that their cases are not connected somehow. It may have had to do with the bank or it may have had to do with an acquaintance they had in common. Diane no longer worked for the bank at the time she was killed.
The details about the car being gone from the mall parking lot, then reappearing, reminded me of the Macon GA case of Carlene Tengelsen in 1972.
http://www.charleyproject.org/cases/t/tengelsen_carlene.html
http://www.macon.com/2009/08/07/802938/the-miracle-of-loss-a-two-part.html
According to Carlene's sister, when they realized she was missing they checked the mall parking lot and the family car was nowhere to be found. The police also could not find it. But later on that night, her sister found the car back in the mall parking lot at 1:45am. No evidence ever turned up about Carlene Tengelsen and it doesn't sound like her case was really investigated at all.
I know that this was 7 years after the disappearance of Mary Little and 5 years after Diane Shields' body was found, but I'm wondering if there could have been a serial killer operating during that time period in GA. I have wondered about Gerard Shaefer but I believe all his known victims were in Florida. However, he could easily have traveled to Georgia to abduct victims.
There is no reason to assume Mary Little's abductor/killer was connected to the Carlene Tengelsen case other than the similarity of the disappearing car from a mall parking lot which turned back up and also the fact that both cases occurred in the same state.
If you check Doe Network and Charley Project for the word "mall" there are quite a few women all across the United States who were last seen in or near a shopping mall. Presumably someone was approaching these women somehow and managing to get them into a vehicle and away from the area. I always think of these type of cases when going to my car in a mall parking lot. It pays to be alert.