Mr Warmbier senior says he does not know exactly what happened to his son during his 17-month detention.
Warmbier's family said they were told by North Korean officials, through contacts with American envoys, that Warmbier fell ill from botulism some time after his trial and lapsed into a coma after taking a sleeping pill, the Washington Post reported.
Warmbier's parents Fred and Cindy have said that they were told their son had been in a coma since March 2016, allegedly after falling ill from botulism and being given a sleeping pill.
Warmbier took questions from the reporters, many of whom asked about Otto's well-being.
Fred Warmbier took to the podium wearing the same cream jacket his son wore during his confession in North Korea.
He called on North Korea to release other American detainees.
Warmbier's parents have been fighting for the release of their son, a University of Virginia student, since his arrest.
Warmbier said even if the North Korean story was true, there's still no excuse for keeping a 15-month coma a secret until last week and denying him access to top-notch medical care.
Congressional women's team hits practice field
He was hit in the left hip, suffering injuries to internal organs, broken bones and severe bleeding, in Wednesday's shooting. That shooting prompted some new security steps, which were not described by officials because they say they never do so.
Warmbier described the family's frustration over having to keep quiet while efforts to release their son went nowhere, and the sense of relief that followed.
He said he felt "anger that [Otto] was so brutally treated for so long" but was relieved his son was "now home in the arms of those who love him".
"I call on them to release the other Americans being held", he urged about three other United States citizens still being detained by the rogue regime.
"North Korea is a Praia regime".
"Otto is not in great shape right now", Fred Warmbier told Fox News' Tucker Carlson in an interview Wednesday.
The US student released by North Korea this week has damage to all parts of his brain, doctors said Thursday.
The 22-year-old University of Virginia student returned to his OH home in a coma earlier this week after spending 17 months in the North on charges of stealing a political propaganda poster.
It was the last time he was seen publicly before this week. "It was kind", Fred Warmbier said.
When asked by a reporter whether he believes President Barack Obama's administration could have done more to secure Otto's release, Fred Warmbier replied simply, "I think the results speak for themselves". He was found guilty of committing a "hostile act" against the country and sentenced in March 2016 to 15 years of hard labor.
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