Investigators in Council Bluffs, Iowa, say Larry Ely Murillo-Moncada, 25, had apparently fallen into an 18-inch (45cm) gap at No Frills supermarket.
Noise from the coolers probably muffled his cries for help, according to investigator Sgt Brandon Danielson.
No foul play was detected and his death was ruled to be accidental.
His body was discovered in January at the store less than a mile from where he lived, but was so badly decomposed that he was not positively identified until last week after a post-mortem examination was conducted.
"You don't hear about these types of cases, [like] people found in walls, especially in this area," said Sgt Danielson, who was assigned the original missing persons case back in 2009.
"We have missing persons all the time, but this is just unique," he told KETV in Omaha, Nebraska, on Monday.
Murillo-Moncada was reported missing the day after Thanksgiving after he fled his parents' house barefoot while suffering hallucinations, relatives say.
He left behind his keys and car, his parents told local media at the time of his disappearance, which occurred during a blizzard.
"He was hearing voices that said 'eat sugar,' " his mother said through a translator in 2009.
"He felt his heart was beating too hard and thought if he ate sugar, his heart would not beat so hard."
The blue clothing found on his body in January matched the description provided by his parents, police say.
The cooler he fell behind was approximately 12 feet tall. He was found by crews that were dismantling shelves in the shop.
Former workers of No Frills, which has been closed for several years, said it was not unusual for employees to scale the top of the freezers to stock goods.
Sgt Danielson said on Monday that his mother had long suspected that he may have been in the store when he went missing.
"The mother, she kind of had an idea that he had never left the No Frills," he said.