My thoughts on NW... gait could be off due to bunions, ingrown toenail, polio as a child, football injury etc etc. Not necessarily military injury, but could be an avenue of thought. I doubt this bloke has any involvement.
A professional hit man, could do the job alone, then text the job is done, and monies electronically transferred. He then could allow whoever to have access to the house to do whatever they desired to do (post mortem). (The terms of agreement could include, "if the person doing the hiring arrived too early to do the staging, he too would also be killed".)
The hitman would remain anonymous, he could control the scene and ensure none of his evidence was left, and might garner more money. A professional hitman would not make it personal. He wouldn't care what happened to those bodies once his money was secured. He wouldn't be in there any longer than necessary, maybe 30 minutes?
The only way I can see the hit being accomplished by one person is that person had a weapon. Secured HS with zip ties, BS arrived next, he secured the zip ties by threatening to harm BS. Barry complied, both thinking they would get out of this alive. They didn't fight, why? At that age what did they have to lose, and I be they thought exactly that way. There had to be a weapon as a threat.
All these so called leaks to KD, really?? If so, why hasn't investigators or KD, thrown a bone to draw the individual to act out? Why hasn't there been a major leak or set up to make the person nervous? Eventually amateurs will make a fatal mistake and goof up, or talk. Ensuring the case does't get compromised is important or tossed out of court due to a slip up by LE, but I am sure someone has a wiley way of making people antsy... if you know what I mean.