I was just listening to the Trace Evidence podcast mentioned above and it reminded me of what
@Kell1 said when I asked him about these murders (he's retired LE). He said that since they found the murder weapon, they found the killer.
The Henry's lived about an hour's drive north of the murder scene. If they did it, they may have known of the spot, but hadn't been there recently.
I also agreed with the podcast host in his discussion of the crime scene and the way the victims were shot. We've discussed this a little before, but it was unique that they were each shot 3 times with the .357. If it was a car/van robbery, that means the killer lived locally, since living victims could describe him/them to LE. Also likely they were already known to LE who might recognize them easily from a victim description.
He brought up another detail I had thought about - why didn't the shooter just shoot them in the head? With a .357, a head shot would have very likely been fatal. Why were they shot in the chest/back and throat? He said it seemed the killer might have wanted them to die more slowly. That might be another aspect to this murder - someone who was not just a car/van thief, but a twisted person who enjoys killing.
The host doesn't mention it, but we've discussed it here - how was the killer able to kill both with such accurate shooting in such low light conditions - dark road, no ambient light, late night, probably only with headlights or a flashlight? Whomever shot them was an experienced, accurate shooter, JMO.
The host brought up the idea that the killer might have been a war veteran. There would have been a lot of veterans at that time - Vietnam, Korea, WWII even. Might even add active duty.
The host also brought up the fact that Lonnie Henry and the guy who discovered the bodies were both truck drivers. He speculated that the Locklair Rd location might have been a spot where local truckers went to hang out, etc.
I'm also inclined to think it was more than one killer, possibly Lonnie and his brother. Perhaps Lonnie went along not knowing the victims would be killed. Was it a buddy of Lonnie's, another truck driver he worked with? Out joyriding, saw a couple with a snazzy van, parked somewhere, sleeping. Decided to watch, then steal the van?