The family of Otto Warmbier, an American college student who died just days after North Korea released him from prison in a coma, declined an autopsy, leaving his cause of death a medical mystery for now.

The Hamilton County Coroner's Office in Ohio examined Warmbier's body after he died on Monday.

"The family's objection to an autopsy was honored, and only an external examination was performed," the coroner's office said in a statement Tuesday night.

In addition to the external exam, the coroner's office reviewed his medical records from the University of Cincinnati Medical Center and AeroMed Management Group, the air ambulance service that helped evacuate him from Pyongyang, North Korea, where he had been detained for nearly 17 months. The coroner's office also had "extensive conversations" with Warmbier's treating physician at the University of Cincinnati Medical Center, according to the statement.

"No conclusions about the cause and manner of Mr. Warmbier's death have been drawn at this time, as there are additional medical records and imaging to review and people to interview," the coroner's office said in its statement. "Our deepest sympathies are with the family and friends of Mr. Warmbier at this time of their tragic loss."

Warmbier, a 22-year-old University of Virginia student, was medically evacuated from Pyongyang and flown to Cincinnati on June 13. He was then rushed to the University of Cincinnati Medical Center. North Korea claimed that Warmbier slipped into a coma after contracting botulism and taking a sleeping pill shortly after his sentencing.

He was arrested at the airport in Pyongyang for allegedly trying to steal a propaganda poster from a restricted area in January 2016 while visiting the country on a sightseeing tour organized by a Chinese-based company. After a one hour trial in March 2016, he was convicted and sentenced to 15 years of hard labor.

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At a news conference on June 15 his father, Fred Warmbier, revealed that President Donald Trump called him a day earlier to ask about his son and the rest of his family. Warmbier said Trump, who was "very candid" during the telephone call, told him Secretary of State Rex Tillerson and other U.S. officials worked hard to negotiate his son's release.

Fred Warmbier told reporters at a news conference that the North Korean regime deemed his son a "war criminal" and "brutalized and terrorized" him during his detainment.

At that news conference, doctors from the University of Cincinnati Medical Center said Otto Warmbier suffered from injuries related to cardiopulmonary arrest and was in a state of unresponsive wakefulness. They said that scans showed extensive loss in all regions of his brain and that they found no evidence of botulism.

"This pattern of brain injury is usually seen as result of cardiopulmonary arrest, where blood supply to the brain is inadequate for a period of time, resulting in the death of brain tissue," Dr. Daniel Kanter told reporters at the news conference.

He said Warmbier was breathing on his own at the time and his vital signs were normal but could not speak or move voluntarily.

"He shows no signs of understanding language ... He has not spoken. He has not engaged in any purposeful movements," Kanter said. "He has profound weakness of contraction in his arms and legs."

According to Dr. Jordan Bonomo, Warmbier had "no fractures to the bone and has minor blemishes on his skin. We see no evidence of an acute or healing fracture."

Warmbier died six days after he was returned home.

"It is our sad duty to report that our son, Otto Warmbier, has completed his journey home. Surrounded by his loving family, Otto died," his parents wrote in a statement Monday.

"Unfortunately, the awful torturous mistreatment our son received at the hands of the North Koreans ensured that no other outcome was possible," they said.

The Warmbiers added that they are "at peace" and "at home."

The funeral service for Otto Warmbier will be held Thursday morning at his alma mater Wyoming High School, in Wyoming, Ohio, and will be open to the public, according to a press release from the funeral home.