North Korea will need to provide an explanation after it released Otto Warmbier, a 22-year-old American who was sentenced to 15 years in prison for alleged anti-state acts, Bill Richardson told CNBC on Tuesday.
The former U.S. ambassador to the United Nations said on "Squawk on the Street" that North Korea must stop taking U.S. citizens and using them as "bargaining chips." He said it could backfire on North Korea "if Otto isn't well."
Richardson spoke after Secretary of State Rex Tillerson said Tuesday that Warmbier, a University of Virginia undergraduate, was released and is "en route to the United States."
North Korea's highest court sentenced Warmbier last year with hard labor after he allegedly attempted to steal a propaganda banner from a restricted area of his hotel.
Richardson, whose foundation deals with political prisoners, said he had heard from Warmbier's parents and they told him the student was in a coma for a year.
"The North Koreans have a lot of explaining to do," said Richardson, head of the Richardson Center for Global Engagement. "Did he get proper ... medical treatment? Why wasn't he released sooner? What is the state of his health right now? He's being flown to Japan where he'll get medical treatment."
—The Associated Press contributed to this report.