The 22-year-old contracted botulism and is in "bad shape" but en route back to the United States, a source close to the family told CNN on Tuesday.
The diplomatic process began on June 6 when State Department Special Representative Joseph Yun met with North Korean UN Mission Ambassador Pak Kil-yon in New York City and learned of Warmbier's deteriorating health condition, according to a senior State Department official.
After that meeting in New York, Secretary of State Rex Tillerson consulted with President Donald Trump and instructed Yun to prepare to travel to North Korea with the intent of bringing Warmbier back to the United States, the official told CNN.
A US delegation made up of Yun and a medical team was sent to North Korea on Monday to secure Warmbier's release, the official said, adding that they demanded to visit Warmbier upon arrival in Pyongyang.
Yun and two doctors visited Warmbier that morning, marking the first time the US was able to confirm his status since he was sentenced in March 2016. Yun immediately demanded that Warmbier be released on humanitarian grounds and arrangements were made for him to leave North Korea.
On Tuesday, Warmbier was evacuated from North Korea, accompanied by a medical team and a State Department representative. He will travel to Ohio where he will be reunited with his family.
The sequence of events leading to Warmbier's release was provided to CNN by a senior State Department official:
January 2016: American college student Otto Warmbier is imprisoned in North Korea.
March 2016: Warmbier is sentenced to 15 years of hard labor.
March 2016 to present: The United States consistently urges that North Korea allow Sweden consular access to Otto and three other American citizens, and pushes for their release.
February 2017 to present: Secretary Tillerson briefs President Trump on the situation. President Trump directs Secretary Tillerson to take all appropriate measures to secure the release of American hostages in North Korea. Tillerson begins the effort and routinely updates the President.
May 2017: US State Department Special Representative for North Korea Policy Joseph Yun meets high-level representatives from the North Korean Ministry of Foreign Affairs in Oslo, Norway, and the North Koreans agree that the Swedish Embassy in Pyongyang will be authorized to pay a consular visit to all four American detainees.
May 2017: After Sweden is granted visitation rights to a detained American, the North Koreans urgently request to have an in-person meeting with the United States in New York City.
June 6, 2017: State Department representative Joseph Yun meets in New York City with DPRK UN Mission Ambassador Pak. During this meeting, Yun learns about Mr. Warmbier's condition.
June 6 to June 11, 2017: After consulting with President Trump, Secretary of State Tillerson instructs State Department representative Yun to prepare to travel to North Korea with the intent of bringing Warmbier back to the United States. The State Department promptly organizes a medical team and an airplane to travel to North Korea. North Korea is informed a delegation will travel to Pyongyang.
June 12: The North Koreans meet the American delegation in Pyongyang and upon arrival State Department representative Yun demands to visit Warmbier. Yun and two doctors visit Warmbier that morning marking the first time the US is able to confirm his status since he was sentenced in March 2016. Yun immediately demands the North Koreans release Warmbier on humanitarian grounds and arrangements are made for him to leave North Korea.
June 13: Warmbier is evacuated from North Korea, accompanied by a medical team and a State Department representative.
A senior State Department official told CNN that the US has not yet accepted the North Korean version of events in terms of the timing and cause of how Warmbier went into a coma.
The US maintains that it had been pressing North Korea to allow Swedish representatives to see the four detained Americans.
Once the Swedish delegation was finally granted permission for a visit, the North Koreans immediately asked for the meeting with Yun.
During that meeting in New York, Yun was told that Warmbier contracted botulism a year ago and went into a coma after taking a sleeping pill, according to the senior US official.
"All we know so far is what they have told us," the official said. "This is the North Korean version of events. We won't know anything for sure until doctors are able to fully evaluate Otto's condition."