Warmbier's team of doctors said they believe his brain injury was not caused by head trauma, but possibly by cardiopulmonary arrest triggered by respiratory failure.
Speaking a news conference, Warmbier's father said North Korea had "brutalised and terrorised" the student and accused it of making false promises that tourists would not be detained. "Since the United States does not maintain diplomatic or consular relations with North Korea, the US government has no means to provide normal consular services to USA citizens in North Korea".
They said they had found no indication of botulism, a toxin that causes nerve damage.
Family says Otto Warmbier has been in a coma since March 2016, shortly after being sentenced to 15 years of hard labour.
The North's KCNA news agency said in a one-sentence dispatch Warmbier's release followed a court decision on Tuesday.
State media in North Korea claims Warmbier was released for "humanitarian reasons".
Veteran former US politician and diplomat Bill Richardson also offered on Friday to visit North Korea to try to secure their release.
The University of Virginia student's father, Fred Warmbier, said his son had been "brutalised and terrorised" by the North Korean government.
"[I feel] relief that Otto is now home in the arms of those who love him", he said. He called on the country to release three other Americans held there. "He has not engaged in any purposeful movements", Kanter said.
Monitoring the Tropics: Two Potential Systems
As of Friday the National Weather Service in Mobile didn't think whatever forms in the Gulf will head for Alabama's Gulf Coast. This broad area of low pressure is meandering around with most thunderstorm activity well to the east in the NW Caribbean Sea.
He called on the administration to find a way to ensure Warmbier "gets the best medical care to see if he can be revived". "The other day I said I won't comment on personal health matters, and so I'm going to stand by that".
"I don't know what being in shock is, but I'm pretty sure I was", he said.
The young man's release came after a flurry of secret diplomatic contacts between Washington and Pyongyang, which culminated in Joseph Yun, the State Department's special envoy to North Korea, travelling to Pyongyang. "I think the results speak for themselves".
Rodman has been visiting North Korea since Tuesday, his latest trip to the isolated state.
Fred Warmbier, in an emotional news conference in OH, did not demur when asked if Obama could have done more.
The developments come amid tensions with the United States following a series of missile tests by North Korea, focusing attention on an arms build-up that Pentagon chief Jim Mattis this week described as "a clear and present danger to all".
He, added: "North Korea should be universally condemned for its abhorrent behaviour".
But the video, released Thursday by Otto Warmbier's brother Austin Warmbier, has become incredibly important to his family.
"Those toughest restrictions on travel and tourism right now only really apply to Cuba", says former Treasury Department official Elizabeth Rosenberg.