Over the next five days, and after consulting Trump, Secretary of State Rex Tillerson instructed Yun to travel to North Korea to negotiate Warmbier's release.
Frank Warmbier said he felt "anger that he was so brutally treated for so long", referring to his son, but was relieved he is "now home in the arms of those who love him".
North Korea sentenced Warmbier, a student at the University of Virginia, to a 15-year prison term for attempting to steal a propaganda poster. Richardson, who has been in close contact with the Warmbier family, said he did not believe Pyongyang's explanation that the student's condition was the result of botulism and a sleeping pill.
Warmbier suffered severe brain damage while in custody.
Earlier, Otto's father, Fred, dismissed whatever efforts were made on behalf of his son by the Obama administration, which asked the family to keep a low profile when news of Otto's arrest became public.
A USA diplomat who traveled to North Korea to secure American college student Otto Warmbier's (WORM'-birz) release also was able to make contact with three other Americans detained there. Warmbier had plans to visit Beijing, China, after he left North Korea.
Warmbier's father, Fred, verbally lashed North Korea, describing it as a "pariah regime" that had "brutalized and terrorized" his son, the New York Timesreported.
Defence Secretary James Mattis declared North Korea "most urgent and risky threat to peace and security", before the House Armed Services Committee, just hours before Mr Warmbier's release was announced. He said the foundation's executive director traveled to North Korea in November and proposed that Richardson travel there for the goal, but the North Koreans did not respond.
"North Korea's continued pursuit of nuclear weapons and the means to deliver them has increased in pace and scope", Mr Mattis said.
Otto Warmbier - a quintessential American guy: tall and good-looking, from a close-knit family in a leafy OH suburb - had joined a group tour to North Korea at the end of 2015 on his way to study overseas in Hong Kong.
Otto Warmbier, a University of Virginia student, was medically evacuated from North Korea and flown to Cincinnati late Tuesday.
Dr. Jordan Bonomo, director for Neurocritical Care Fellowship at the University of Cincinnati, said respiratory arrest is the main cause of cardiopulmonary arrest in a young person, and respiratory arrest is typically caused by "intoxication or traumatic injury". "No other family should have to endure what the Warmbiers have".
"It must have been an accident and that's probably why they were hiding it for a year", Go Myong-Hyun, researcher at the Asan Institute for Policy Studies, told AFP.
One of Obama's advisers, Ned Price, said the Obama administration had "no higher priority" than securing the release of Americans detained overseas but North Korea's isolation "posed unique challenges".
"We have very few answers", Fred Warmbier said.
Rodman created a stir by arriving in the country with his small entourage all wearing clothing and hats featuring the name of a company specializing in a cybercurrency used to buy and sell marijuana. "The results speak for themselves".
Doctors said they examined Warmbier's body and saw no evidence of fractures that might be evidence of severe beatings.
State Department officials refused to comment on Warmbier's health, citing department guidelines, but said the last time the USA had any access to Warmbier, through the Swedish Embassy, was March of previous year.
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