I've started going back over the basics again, for myself. Rewatched the original video, took screencaps and so on. Still, couldn't get any closer to a close up of the SP's face.
However, I realized that I'd been making an assumption about the SP's girth. He or she is not a large/heavy person at all. This has probably been covered extensively by others here. But just for my own piece of mind, I worked on the SS myself to understand what I was seeing. I think SP is carrying some kind of mini backpack/satchel on his/her front. That's where most of the tools would have been kept. Within easy reach. Perhaps they are a lot thinner than most might think.
I've delved into places online I sorta wish I hadn't, but I did find some interesting info which led me to consider a different possible suspect than I'd had in mind previously.
While I can't go into details because of the rules, perhaps I can ask some questions which might help solidify my theory while not crossing over the line.
1) Is it legally possible to find out who were dispatched out to the crime scene that evening? Both MPD and MFD (was it Midlothian in both instances?).
2) What if the SP has connections to law enforcement via family, but also has ties to the fire department?
3) What if the SP was fully prepared to return to the crime scene as part of the first responders, in order to ensure any potential DNA left behind during the murder could be ruled out?
4) What if SP was of a younger generation, but very conservative in values and angry at the potential impending destruction of their family unit due to MB's actions/influence (might just be perceived and not actual)?
5) What if SP had ties to the CCoC via a family member and thus was somewhat familiar with the layout/cam positions etc?
6) What if SP was acting on behalf of his/her family, potentially with an accomplice as driver/scout.