The family of Otto Warmbier has declined an autopsy, leaving the cause of the American college student's death a mystery.

Warmbier, 22, died on Monday, less than a week after he was released from North Korea in a coma. Officials at University of Cincinnati Medial Center, who treated the student upon his return, labeled his condition as a "state of unresponsive wakefulness," suggesting that he had lost blood supply to his brain for a period of time.

The office of Hamilton County Coroner Dr. Lakshmi Sammarco reported Tuesday that only an external examination was performed on Warmbier's body, per his family's request. The office reviewed medical records and talked extensively with physicians who treated him.

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Fred and Cindy Warmbier announced their son's death in a statement on Monday.

"It is our sad duty to report that our son, Otto Warmbier, has completed his journey home. Surrounded by his loving family, Otto died [Monday] at 2:20 p.m.," the Warmbiers announced.

"It would be easy at a moment like this to focus on all that we lost - future time that won't be spent with a warm, engaging, brilliant young man whose curiosity and enthusiasm for life knew no bounds. But we choose to focus on the time we were given to be with this remarkable person," the statement read.

Fred and Cindy Warmbier thanked the medical team at the hospital, but added "the awful torturous mistreatment" their son received ensured that there was "no other outcome possible."

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The University of Virginia student was accused of trying to steal a propoganda banner when he visited North Korea with a tour group last year. He was sentenced to 15 years of hard labor.

The North Korean regime told U.S. officials that Warmbier had botulism, a strong neurotoxin produced by bacterium, and slipped into a coma after taking a sleeping pill about a month into his sentence. Doctors, however, found no evidence of botulism.

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"He has spontaneous eye opening and blinking," Dr. Daniel Kanter, director of the hospital's neurocritical care program, said last week. "However, he shows no signs of understanding language, responding to verbal commands or awareness to his surroundings."

Kanter added that scans showed no evidence of a "traumatic brain injury," and that Warmbier's state was likely a result of a cardio or pulmonary arrest.

Fox News' Shira Bush contributed to this report.