On Tuesday, Otto Warmbier returned home to the United States in a coma after spending 17 months as a political prisoner in North Korea. The official report from North Korean officials explained that the University of Virginia student, who was imprisoned for tearing down a North Korean propaganda poster, contracted food-borne botulism shortly after giving a press conference in June 2015 and then fell into a coma after taking a sleeping pill.

Update, June 19: Otto Warmbier’s parents announced their son has died at age 22..

But what American doctors found while completing a full medical examination on Warmbier casts serious doubt on the North Korean report.

In a press conference on Thursday at the University of Cincinnati Medical Center, where Warmbier is being treated, Dr. Daniel Kanter reported that his patient had “extensive loss of brain tissue in all brain regions.” The pattern of brain injury shown by Warmbier’s MRI scans, he explained, was consistent with “cardiopulmonary arrest, where the blood supply to the brain is inadequate for a period of time, resulting in the death of brain tissue.”

There is speculation that Warmbier’s brain injuries were caused by physical abuse in North Korea. The New York Times reported that an unnamed senior American official said Warmbier was “singled out for particularly brutal beatings while in captivity,” hinting at a much more violent cause for Warmbier’s injury. Warmbier’s parents have stated they do not believe the official story, and are convinced that their son was “brutalized and terrorized.” But in the press conference, Kanter said that the medical team had found “no evidence of an acute or healing fracture, including the skull.” He added that the pattern of brain injury was “not the type we normally see with traumatic brain injury,” reiterating that the evidence pointed to cardiopulmonary arrest.

Otto Warmbier sustained "extensive loss of brain tissue in all regions."

Cardiopulmonary arrest — which is a failure of the heart to continue beating, and is different from a heart attack — is not a common condition in young, otherwise healthy people, said Dr. Jordan Bonomo, another doctor at the conference. He explained that if one occurred, it was likely caused, in turn, by respiratory arrest — when breathing stops. Respiratory arrest is also a “rare” event in a young person, he noted, and when it happens it is likely caused by “intoxication” or “traumatic injury.” The medical team did not indicate, however, what they think ultimately caused Warmbier’s brain injury.

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Why Was Otto Warmbier Detained in North Korea?

They were skeptical of the botulism story, as some other experts have expressed. Kanter said that his team didn’t find any evidence in Warmbier’s nerves that botulism was active. Dr. Brandon Foreman, another doctor who spoke at the conference, was also asked to confirm that Warmbier’s tests showed no evidence of botulism. “That’s correct,” he replied.

Their report calls into question the veracity of the North Korean medical report, but the doctors were hesitant to speculate. Foreman said they had “absolutely no information” about the type of care Warmbier received in North Korea, but Kanter noted that when Warmbier arrived his skin was “in good condition,” and he was “well nourished.” They stated that he arrived with a disc containing two MRI scans dated April and July 2016. These MRI scans, Kanter explained, showed that the brain injury had likely occurred in the “preceding weeks” before they were taken. Comparing Warmbier’s most recent MRI to the North Korean scans, Kanter said that they are “consistent with tissue evolution, not new damage.” Tissue evolution, in this case, refers to the body’s natural housekeeping mechanisms attempting to clear out the damaged tissue in the brain.

Currently, Warmbier is in an “unresponsive wakefulness state,” in which he shows “no signs of understanding” and lacks “consistent and persistent responses to his environment,” said Dr. Brandon Foreman, who also spoke at the conference. In an agreement with Warmbier’s family, the doctors are making all information about his prognosis, improvement, and future care confidential.

Warmbier’s family has spoken out, however. As the New York Times reports, in a press conference at Wyoming High School, Otto’s father Fred Warmbier said, “Even if you believe their explanation of botulism and a sleeping pill causing a coma — and we don’t — there is no excuse for any civilized nation to have kept his condition a secret and denied him top-notch medical care for so long.”

Photos via Getty Images / Bill Pugliano