I'm still really 50/50 on the B&E vs. planned murder. The thoughts I keep coming back to are:
If the murder was a planned attack, the ideal murder weapon was not brought along. We have no indication of a firearm being used - puncture wound is not how you describe gun-shot wounds. If it was a planned attack, and indeed a gun was not used, there is a reason for that - zero gun experience, a felony, small house/children where hiding a gun might be difficult, unable to use existing guns in the household for some reason, unable to purchase a gun without being noticed, unable to get far enough away from home to purchase a gun unnoticed. This is Texas - where gun culture is pervasive and it's not uncommon for most households to own at least one firearm. Therefore, I'm looking for suspects who are unlikely to have access to a firearm in a situation where a firearm would be literally (or subjectively) most efficient.
If this is a B&E, it's not a regular burglary. I see a relaxed, "show-boating" attitude, sauntering around, having their way in an empty building. Doesn't look like SP cares too much about any "target" in the building. I'm not trying to weave some tale, but this looks like it could be a "thrill" b&e ritual. SP dresses up like this and breaks into buildings from time to time. Sometimes destroying property, sometimes stealing something opportunistically, sometimes making a sandwich. SP thinks they are stealthy and they have a late night secret. Like a cat burglar. SP thinks he/she is smart by having their "go-costume" that over time they've put together to be perfect. In this scenario we have a surprise confrontation on the other side of the building between MB and SP where a chase occurs (back toward the SW side of the building) where SP freaks out and kills her. This is the first time someone has interrupted them on one of their late-night rituals.
I walked in on a burglary in progress in my home in February. I came within about 5 feet of the guy and while he swung his giant wrench/break-in tool at me and ran after me as I tried to escape my house he ran directly past me and out into the alley to his car. Burglars down't want to get caught. They want to get out. They engage only if prevented from escaping or if it's a heist way beyond a home/church burglary.
Weirdo cat burglars who have this late-night power trip secret would want to neutralize someone who could bring everything crashing down.