The 22-year-old University of Virginia student died in June, six days after returning from North Korea with severe brain damage. He had been sentenced to 15 years hard labour after travelling in January 2016 and allegedly stealing a propaganda poster.
On Tuesday, his parents broke their silence on their son's tragic death, saying he was subject to "inhuman" suffering from the "terrorist" nation.
"We're here to tell you North Korea is not a victim, they're terrorists," Otto's father Fred Warmbier said. "They kidnapped Otto, they tortured him, they intentionally injured him."
Mr Warmbier said the first time they saw Otto after he arrived back in the US their son was making a "howling involuntary, inhuman sound".
"We weren't really certain what it was. We climbed to the top of the steps, we looked in and Otto was on the stretcher across the plane and he was jerking violently making these inhuman sounds.
"Cindy and Greta ran off the plane. Austin and I walked over to Otto. He had a shaved head, he had a feeding tube coming out of his nose. He was staring blankly into space, jerking violently. He was blind, he was deaf. As we looked at him and tried to comfort him. It looked like someone had taken a pair of pliers and tried to rearrange his bottom teeth."
The couple also shared their story with CNN, saying "his bottom teeth looked like they had taken a pair of pliers and rearranged them."
"That's why they released him, they didn't want him to die on their soil," Cindy Warmbier said.
The appearance led to President Trump tweeting that "Otto was tortured beyond belief by North Korea" amid a critical point in relations between the two countries.
The coroner's findings are consistent with remarks made by Cincinnati doctors in June, who found no evidence of trauma or fractures after examining Warmbier immediately after he arrived in the US. He was found to have extensive brain damage similar to that shown when people suffer a heart attack that cuts of blood supply to the brain.
At the time, Dr Daniel Kanter said Warmbier's condition was stable on arrival with no signs of "infection or dysfunction of major non-neurological organs".
"His neurological condition can be best described as a state of 'unresponsive wakefulness'," he said. "He has spontaneous eye-opening and blinking, however he shows no signs of understanding language, understanding verbal commands or awareness of his surroundings. He has not spoken. He has not engaged in any purposeful movements or behaviours."
Doctors said the most important diagnostic test was a brain scan that showed "extensive loss of brain tissue in all regions of the brain", but admitted they had no certainty about how it occurred.
"We have no certain or verifiable knowledge of the cause or circumstances of his neurological injury. This pattern of brain injury however is usually seen as a result of cardiopulmonary arrest where the blood supply to the brain is inadequate ... resulting in the death of brain tissue."
North Korea have denied mistreating Warmbier, claiming he suffered from botulism, a rare condition where bacteria attacks vital organs. Doctors found no signs this was the case.
