I think the FBI is going to prove otherwise and it was there.
This is an interesting site.
http://www.crime-scene-investigator.net/excavation.html
Collection of unburied surface remains
Exposure to the climate accelerates decomposition and destruction and thus it is essential that unburied bodies be removed as soon as possible. Buried bodies are usually not accessible to animals, insects or changes in surface temperature, therefore, the rate of decomposition relies solely on the activity of microorganisms and soil structure. In the case of single or shallow graves, the process of decomposition is usually more rapid, while in mass graves where bodies are usually packed very tightly and there is little oxygen to promote growth of organisms and decomposition the bodies may stay well preserved. Unburied bodies are exposed not only to the destructive effects of climate but also animal activity. The potential for animals to destroy or scatter body parts
increases with time. The number of bones missing directly correlates to the time elapsed since death. Exposure to environmental elements for prolonged periods also decreases the prospects of positive identification.
I also read that when a body has been placed in a plastic bag it will seal the odor in until the animals come along later and disturbs it. By that time many times decomposition is in its last stages and the smell would no longer be putrid.imoo