Location of JRs body:
If JRs body was lying in such an exposed location, beside a roadside, in an area near to one of the focuses of searches, how was it not discovered earlier? Helicopters were scouring open spaces for several days prior to her discovery, eventually by trash collectors from the road.
1. She was not placed there until near to the time of discovery.
2. She was placed in the culvert, and was subsequently moved by animals.
3. She was placed there, but animals made her location more obvious, by tearing at a garbage bag for instance.
What was the state of decomposition of her body? This would obviously help to pinpoint time of death and help narrow down timeframes to trigger witness accounts. What could hinder these calculations is lack of knowledge of how long her body had been exposed to elements that accelerate or hinder decomposition.
I imagine they could also analyse the state of digestion of the Granola Bar JR had for breakfast the morning of her disappearance. Could this be used to determine time of death? If little digestion had occurred, at least her ordeal was relatively short. If fully digested, would this indicate that she was alive for some time? Or does the body continue to digest post-mortem.
SBM
I agreed with the vast majority of your post and snipped out what I wanted to add comments on.
Depending on the exact location of Jessica's remains in relationship to the road and the state of those remains, it may be that it was placed there as soon as Friday (more likely after dark).
In my experience, people vastly overestimate how much they see when they are driving. Even if the car is just creeping along at 10 mph, a passenger tends to have the illusion they can see everything they could if they were walking but they really can't. My impression is that the stretch of road Jessica's remains were found on had a speed limit much higher than 15 mph, maybe as high as 55 mph (locals?).
If her remains were such that they didn't form the outline of a human body or the angle in relationship to the road was such that people on the road didn't see the outline of a human body, then many people could have passed her remains without realising it. For instance, people tend to readily catch a full frontal or full rear outline of a body but do not easily identify a body seen from the angle of the feet looking towards the head.
Also, drivers should be paying attention to the road. If her body was visible near the road, then I'm actually pleased that drivers didn't spot it because that means they were paying attention to driving. I don't know about Colorado but in Iowa, this is the time of year when many animals are spotted or killed on roadsides because the young animals have mostly left their mothers and all the animals are travelling to forage before winter sets in. Drivers should never forget that they are controlling a large and potentially lethal machine that warrants close attention to what they are doing.
As for digestion, it slows down and stops within the first 30 minutes or so of death. It does depend on age, on the person's body mass, on what was eaten, activity level after eating, etc. It can vary widely.
Time of death can be estimated but it is only an estimate and may not be even remotely correct, depending on the specific circumstances.
For instance, my father is an anesthesiologist and I clearly remember him describing one case he saw in surgery. A man whose ulcer had created a lot of scar tissue such that it blocked off the outlet of the stomach waited several days to see his doctor and had rather non-specific symptoms. My father was amazed to see the surgeon remove the clearly recognisable remains of the whole orange that the patient had eaten 8 days prior to the surgery. My father said that it looked and smelled like an orange with very little digestion evident.
The patient survived the surgery and I hope he enjoyed telling the tale. It was certainly a strange incident but it illustrates that food can survive inside a human stomach for quite a long time without showing significant evidence of digestion. If that man had been killed 7 days after eating that orange, his time of death would probably have been estimated as occurring within hours of eating the orange but that would not be correct.
Eventually whatever was in the digestive tract will decompose along with the body but decomposition is distinctive from digestion.