My theory has always been that Barrentine ran into the killers when he was out for milk. This explains why he was gone so long. I think he knew the killers, either from school, or just living in Ozark. I'm not convinced that BS was not the killer or was with them. Barrentine happens upon them after they are talking to, or have subdued the girls. He's just a bumbling, friendly guy who likes to impress. he sees the guys and goes over to speak to/ hang out with some cool guys before completing his errand. Oops, now Barrentine knows what they are doing. So what do they do? They threaten him into helping them and he does. Maybe threatening him is enough, or maybe they threaten his wife or child. Either way, he goes along with them and parks the car on Herring St. He gets home late, he's all shook up.
This explains his fascination with the case.
In the meantime, the actual killers go on home, they have the connections , or street smarts to not get caught, looks like Barrentine will be their patsy and take the rap when he is arrested.
Barrentine might have told his wife what really happened. He might have told a family member what happened. They know he is not real bright. They know he wasn't a killer, so they protect him for the rest of his life.
This theory leaves the door open for it to have been several suspects. BS, or the guy that went to MI, or even someone whose name has never been brought up. I have always believed it happened this way. The killers couldve even been LE impersonators but Barrentine knew them and stopped .That would explain the license being left out and the drivers window being partly down.