Agree with almost all of this but need to add two things .
1. My door I get alerts . So no monitoring needed . If someone enters I know bc I get an alert of who it is . Also we can send the phone ap so others can open my door . With that you need no code it opens with your phone in front of it. This would explain the door opening but chain locked so NU could see inside . SW IMO gave her that app . Which could also mean she expected something bad or she simply had it bc they lived near each other and were business associates so used it sometimes .
2. The moniter most likely has night vision so that is crucial being what his defense would say “she turned the lights on to do it” at this point color images would be on screen . As an example ,this is a low end model
Summer Infant - Baby Video Monitors
I am hoping they had the one connects to a phone app so she could view kids from it or one that records like a nanny cam footage police could use to show footage from it .
I think he is guilty so please don’t see me as rude I’m just trying to think of all possibilities