A 2014 landmark report by a United Nations investigators catalogued massive human rights violations in North Korea which they said could amount to crimes against humanity. North Korea claimed it had released him on "humanitarian grounds", without providing specifics of the situation.
"We have no certifiable knowledge of the cause or circumstances of his neurological injuries", Kanter said.
Warmbier was on a tour of North Korea early past year when he allegedly tried to steal a propaganda banner from his hotel and was charged with hostile acts against the state.
Fred also said ex-NBA star Dennis Rodman's ongoing trip to the reclusive country did not aide in his son's release.
North Koreans charged it was at that point Warmbier allegedly went into a staff-only area of the hotel and tore down a propaganda banner hanging on the wall, intending to steal it.
His family said he had been in a coma since March 2016, shortly after he was sentenced to 15 years' hard labor in North Korea.
The retired basketball player said before leaving for Pyongyang last week that his mission was to try to build bridges between the USA and the reclusive state.
Doctors remain uncertain about the exact cause of Warmbier's condition, yet his family does not believe North Korea's claim that he fell into a coma after becoming ill with botulism and taking a sleeping pill.
The father saluted his son as a brilliant, adventurous and courageous man who did what he could to endure brutality and terror.
"We're going to leave that to the doctors (to explain) today", he said. "He has profound weakness of contraction in his arms and legs". Beyond minor skin blemishes consistent with medical care they found no evidence of fractures or trauma to his body.
"He has spontaneous eye opening and blinking", Dr. Daniel Kanter, who is head of the hospital's neurocritical care program, told reporters on Thursday. "We did not find any evidence of that". Joseph Yun, Washington's special envoy on North Korea, added they were working to secure their freedom as well.
Doctors said they have very limited information about Warmbier's condition before his arrival in the United States and have not had any contact with North Korean medical officials.
"Otto has been terrorized and brutalized for 18 months by a pariah regime in North Korea", the father said in an interview with Tucker Carlson of Fox News that aired Thursday night. He was released six days later.
Fred also said they had asked the previous administration to handle Otto's case but failed to get any progress. I think God hears our prayers'.
"In terms of their medical condition, that's something I can not comment on", said State Department spokeswoman Heather Nauert.
The U.S. says North Korea is using detained Americans as political pawns, while Pyongyang has accused Washington and Seoul of sending spies to overthrow the regime.
"Those toughest restrictions on travel and tourism right now only really apply to Cuba", says former Treasury Department official Elizabeth Rosenberg. At that trial, Otto Warmbier described his actions as "the biggest mistake of my life". Three other US citizens are being held by the regime; President Trump should make their release a priority.
"There are three other Americans now being held in North Korea".
Rodman also visited iconic North Korean monuments and coached a women's basketball team.
They declined to discuss his prognosis or speculate about the future, at the family's request.