I didn't follow much of this case after the father was arrested. Seem to remember it being one of several cases where the child disappeared while in a car.
This happened during the time when most of this country and LE were still in an uproar about the not guilty verdict for FCA. Perps began using all kind of wild stories to cover their actions and LE was determined not to be hoodwinked by them.
If the car is still in possession of LE, another dog search could be done to confirm the original findings and maybe a new search for fingerprints.
Unless her body is found, I'm afraid there will always be someone who will not believe the verdict.
...The key to the conviction was a cadaver dog brought in by police. The dog sniffed the crime scene and barked, indicating the presence of a dead person...