IMO, his story mostly checks out. I'm aware of stats that point to husbands and there are numerous cases that everyone can point to as backup. Here is what I don't find suspicious about him:
SW going away for 6 weeks without him - summer vacation, he wasn't able to go because work. Her work and scheduled afforded that long of a trip. Doesn't point to marital strife.
No grief in interview - I've said this a few times, everyone processes grief differently. If he processes things internally and within an inner-monologue, he would seem to be devoid of emotion because he's processing. As someone who has experienced a lot in this area, I don't think this should automatically raise alarms.
Body positioning during interview (arms across chest) - It's a defensive posture, yes. Tell me how comfortable you would be if you were going through an intense and stressful situation and you were being interviewed on camera. If my pulse on him above is right, he's probably an introvert and feels very uncomfortable being interviewed.
"Heated discussion" - Yes, this happens often in marriage. I think he mentioned it because he wants to say that their marriage wasn't perfect, I think he's being forthcoming.
Neighbor Camera - If it's far enough away and at night, it's possible that movement couldn't be accurately seen. More on that below.
IMO, the only thing that points to him is the fact that there isn't an image or anything that suggests SW and her kids leaving. There isn't an image that suggests anyone came or left IIRC. From friends who have posted, it sounds like their marriage wasn't perfect but it seems normal. I don't buy much that I see on SM because we all clean up our lives for our posts.
