I understand what you are saying DK but I have to admit I find it a little baffling that Terry was not found for a few hours. Surely local police knew who Darlene and Terry were and with Terry not in the house instead of assuming he killed her and took off you would think they would search the surrounding buildings, the property with dogs, etc. Not only to look for Terry but also to look for any signs of the killers.
The lack of blood trail is baffling. Blind Luck? There was no blood transfer between Terry and Darlene meaning either two weapons were used or the killer wiped it clean and then went to kill the other. No sign of the killer walking between the two crime scenes......it sounds more and more like there were two killers that night, each one killed seperately, never crossed paths - the one inside never went out, the one outside never came in. The one that committed the robbery either had to do it after he changed or he left, changed, showered etc and then came back. Perhaps the robbery was an afterthought? He/they went there with the intent to kill them for some reason, left the scene and then a few hours later decided, what the hell? I might as well go back and steal what I can.
I just don't see how there could have been one killer. If there was then why did he obviously go to great pains not to connect himself to both of the bodies. He would have had to change clothes, shoes -- or at least put bags over his shoes or something, completely clean the weapon off and then do the same thing again after Terry's death. Why? It doesn't really make sense.
What Roscoe said about hunting coveralls makes sense. You could easily zip into one of those and protect your clothing, take it off, wrap it up and stick it in your back pack which you burn asap.
There was forensic evidence left behind though, right? We just don't know what it is?
