This thread piqued my interest and DH and I just finished watching this On Demand. My DH, who is not the most observant person regarding certain things, immediately identified that there is an improper relationship between Dan Schuler and the SIL. So he is in agreement with some of the prior posters on this matter.
We both have a couple questions regarding the incident because we didn't follow it at the time. When do the investigative authorities think Diane smoked the pot? Do they think she got out of the car to smoke it? Did they ever get confirmation from the family that she had it in her possession during the weekend? Either she had it or stopped and got it, correct? Dan stated that the Absolute bottle came from the camper, but was that confirmed during the investigation? Seems strange that she could drink out of an alcohol bottle and smoke pot in front of the older children and them not think anything about it. You would think that the older child, when she made the phone call, might say something about her behavior, especially considering how noxious pot smoking smells.
The other confusion is that the documentary doesn't really lay out the timeline very well. Exactly how much time is unaccounted for considering the stops at McDonald's, the gas station and the bridge? Do they have any theory about what happened during any unaccounted for time?
Also, the phone call from the private investigator Tom to the SIL. Is it implied that the attorney and the husband had those results all along but were telling everyone else that the PI was not releasing them? I thought he implied that but really didn't come right out and state that Dan knows this but is in denial. He keeps asking her "where do you think you go from here?" almost like a therapist would. I got the impression that he is fed up with the family because they aren't accepting of the facts.
Seems incredibly far reaching that the family wants to implicate a tooth that has been troublesome since 2005, 4 years prior. And the husbands comment that he has no time to himself makes me sick.

The interview was somewhere between 6months and 1. 5 years after this event. What on earth would he need alone time for when the only thing he has in the world left is his son?

What's he wanna do with that alone time? And as his SIL stated, he has all day while his child is at school.