A lot of first class sleuthing going on on this site. I hope my contribution is up to the standards you all have set.
For whatever it is worth, I offer up the following observations:
1) As in any homicide investigation, a certain amount of "investigation" must be conducted on the victims. An adequate investigation would require that any chance that the seman got on B.J.'s undies through "innocent means" be ruled out 99.9%. (in 1999, there was no way DNA could be obtained from fabrique after it had been washed). We have to be able to assume that this was done and we can conclude that the DNA belong to the killer..
2)I am satisfied that the narrative that they blundered into Ozark accidentally while trying to find the party or find their way back is essentially accurate. If they had some unknown reason to go there, it is irrelevant to solving the crime. By asking Mrs. Merritt for directions back to Dothan, they established that they were in a town they were unfamiliar with and they were intent on returning immediately. The odds of encountering someone they knew who meant them harm is virtually nil. The were victims of a stranger sexual predator.
3) There is a pattern of sexual homicide where the perp abducts the victim by vehicle at one site, goes to a second site where the rape or whatever is committed and then dumping the victim at a third site. This isn't terribly imaginative but it can be very effective and many unsolved sexual homicides fit the pattern. The key is that as long as the perp can keep LE from identifying the "rape", the perp is free to use a spot that he is very comfortable with without fear that it can be linked to him. Also, forensic evidence that may be left at this site would not be a problem. Very often, finding the "rape site" is key to solving the crime.
The fact that the girls pant legs were wet would be a key clue to this site. It is not clear how wet they were. Pant legs wet by walking through dewey grass would be dry after they had sat, in summer heat, in the trunk of a car until 2:00PM the next day. Presumably they were in standing water. How deep? (one report said it was almost up to their waists) The only reasons for this that I can think of is that they either had to walk through water to get to the rape site or the perp wanted them to wash off some evidence (perhaps mud) from their feet or legs. Goggle Earth shows some small ponds in the area. Were they all checked out?
4)According to Jon Douglas, young or inexperienced sexual offenders may "fail to preform" and will resort to masterbation. The guy planned and executed the abduction well but it was probably his first time and his "failure to preform" might discourage him from doing it again. This might be the only sex crime this guy did.
5)I'm pretty sure our perp left his own vehicle on East Broad st; probably near Depot. He left the Mazda on Herring because it was within walking distance and no one would see him leaving the car. Until the actual abduction, he had no way of knowing in advance that he would need to have a discrete place to abandon a vehicle that night. Still, he knew about Herring St which, from what I can tell is a pretty obscure spot. Soldiers on base will venture into town for shopping and entertainment, but I don't see a reason many would be familiar with that area. I'm betting the guy was a local.
6)It is extremely likely that the White Truck is the perp's vehicle. The drivers behavior is "odd" but it is consistent with someone checking out the girls at the phone both and the guy never came forward. The trouble is, if Alabama is anything like Texas and Louisiana, where I have spent some time, very many men of all ages drive Pick Ups and most of them are white. Enhanced photography might have helped at the time to identify more details but it may not have been available or practical. At this point, it is probably too late to identify the truck .
7)The fact that the guy didn't go through the girls purses an take whatever cash there was is a little unusual. Most Sexual predators would in that situation. It is suggestive that the guy did not routinely engage in property crimes and he was not in any particular need of money. He was probably employed and did not have a "criminal" reputation. I don't know what crimes you need to commit in Alabama to get your blood drawn for DNA, but it seems like he hasn't been caught doing such a crime.
Overall, my WAG (wild *advertiser censored* guess) is that the guy was local and either still lives they or has family he is touch with. He has managed to avoid the kind of trouble that gets your DNA profile on data bases and will probably get away with it if he can stay clean.