Also, if B&H had an alarm system, but they didn't arm it unless they were gone from the house, it would make sense that the alarm was turned off when H arrived home and was never re-armed. Not like the killer would set the alarm after himself, right?
Although it is interesting that the door WAS locked. We have understood that the couple left the door UNlocked, but yet the couple was inside the home and the door somehow became locked sometime between when H arrived home on Wed evening and before the cleaning lady arrived on Friday morning. Was it one of those locks where you can just twist the little button on your way out and it locks the door, or was it a deadbolt requiring a key to lock from the outside?
ETA - if it was one of the button locks that can lock from the inside on your way out the door, did that unknown person ever enter the home (the one the neighbors have on video I believe, and was there for something like half an hour, I believe on the Thursday?), and possibly lock it on his way out after calling and finding nobody responding, or did he just hang around the doorway(s), hoping someone would answer the door?