Sevier County Sheriff Office Capt. Jeff McCarter told the Knoxville News Sentinel that firefighters and investigators spent several days sifting through debris searching for any trace of Tyveon Temple of Indianapolis.
"The anthropologists told us there was a great possibility the factors involved would create a complete incineration of someone that size," he said. "Generally, we usually find some remains but they are always larger people, adults. Body mass has a lot to do with that. This child weighed approximately 40 pounds."
Other factors cited were the amount of heat generated by the blaze and its duration. McCarter said a natural gas line ruptured during the fire and created fuel for the flames.
"They told us it was a great possibility (those factors) created a complete incineration of someone that size," he said. "That's the only explanation."
The fire broke out April 12 at a Sevierville cabin where 22 people from Kentucky and Indiana were staying.
One other person, 56-year-old Ricky Hudson of Indianapolis, died after suffering severe lacerations from breaking a window in an attempt to save others. Hudson was the boy's step-grandfather.
McCarter said deputies used tracking and cadaver dogs to search the area around the cabin for the remote possibility that the child escaped unnoticed, but nothing was found.
He said anthropologists used screens typical for excavating a burial site.
"They were unable to find anything," he said. "They sifted all the way to the dirt and spent five days pouring it out in buckets, every bit of debris to no avail."
The cause of the blaze was still under investigation.