KEY POINTS
  • Bill Richardson tells CNBC North Korea's choices could backfire.
  • "The North Koreans have a lot of explaining to do," he added.

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."