Two ambulances were parked near an airport hangar.
Department of State spokeswoman Heather Nauert told reporters Rodman had nothing to do with Warmbier's release.
Richardson, a Democrat, credited the Department of State with securing Warmbier's return from North Korea without any preconditions but said a forceful response from the USA government would be required "if its determined that there was a cover-up and Otto's condition was not disclosed and he didn't get proper treatment".
Otto Warmbier speaks at a news conference in North Korea, in 2016.
Americans are regarded as enemies in North Korea because the two countries never signed a peace treaty at the end of the 1950-53 Korean War.
The arrests have come at a time of heightened tension between North Korea and the U.S. and its regional neighbours.
The 22-year-old University of Virginia student was medically evacuated from North Korea and flown to Cincinnati late Tuesday.
The State Department denied any connection between Warmbier's release and Rodman's visit, which the Trump administration said it did not authorise.
Before his trial, Warmbier had said he tried to steal a propaganda banner as a trophy for an acquaintance who wanted to hang it in her church.
'We've been praying for him, his parents, and now the people transporting him back home, ' Miller said after Warmbier's release.
His parents, Fred and Cindy Warmbier, said: "We want the world to know how we and our son have been brutalized and terrorized by the pariah regime". 'The journey for them has been very hard, to say the least, and they still need our support and love'.
In Warmbier's hometown of Wyoming, just outside of Cincinnati, residents helped tie blue and white ribbons, Wyoming High School's colors, to trees and said news of his release had sent waves of shock and joy through the community.
Rodman, who endorsed presidential candidate Donald Trump during the 2016 election campaign and appeared twice as a contestant on Trump's "Celebrity Apprentice" TV show, said his latest visit was merely created to visit old friends and to "have a good time". The official referred to them as "hostages".
North Korea regularly accuses Washington and Seoul of sending spies to overthrow its government to enable the USA -backed South Korean government to take control of the Korean Peninsula.
US officials appeared to brush aside any speculation of a connection between Rodman's controversial visit and Warmbier's release. Rodman has traveled to the isolated nation four times since 2013, attracting a lot of publicity, much of it unfavorable.
The announcement comes as former National Basketball Association player Dennis Rodman is paying a return visit to North Korea.
President Trump has been soft-pedalling his public stance on China in the hope that Beijing will force Pyongyang to abandon its nuclear programme.
Pinkston said the trip was likely part of an effort by the North's foreign ministry to ease tensions with Washington.
There was no immediate confirmation from USA officials of North Korea's description of his illness.
Previous detainees have been released after visits from high-profile Americans, including former presidents Jimmy Carter and Bill Clinton. He worked at the Pyongyang University of Science and Technology.
Tony Kim, also known by his Korean name Kim Sang Duk, was also a teacher at PUST. He was accused of committing unspecified criminal acts meant to overthrow the government.
The family said it was told by North Korean officials, through contacts with American envoys, that Warmbier fell ill from botulism sometime after his March 2016 trial and lapsed into a coma after taking a sleeping pill, the Washington Post reported.
But North Korea has so far rejected South Korean civic groups' bids to visit the North for exchanges, taking issue with South Korea's support of the latest United Nations sanctions.
The United States had accused the North of using Warmbier as a political pawn, condemning the sentence as far out of proportion to his alleged crime.
Warmbier's parents were told their son was given a sleeping pill soon after his trial in March a year ago and never woke.
Warmbier's release came as former USA basketball star Dennis Rodman arrived in North Korea on Tuesday, returning to the increasingly isolated nuclear-armed country where he has previously met leader Kim Jong Un.
US Secretary of State Rex Tillerson.