The parents of Otto Warmbier are asking U.S. courts to allow them to go after North Korea's assets to enforce a $501 million judgment against the country.

A federal judge ruled Dec. 24, 2018, that North Korea is liable for the torture and death of Warmbier, a University of Virginia student from Wyoming, Ohio. The order demands the money go to Fred and Cindy Warmbier and their son's estate.

Warmbier's parents argue in a March 26 federal court filing that "a reasonable period of time has elapsed" since the judgment and when it was served Feb. 14.

More:Five things we learned from the Warmbiers’ court victory over North Korea

The proposed order would grant the Warmbiers the ability to collect on the judgment by any means permissible under federal or state law "against the assets of North Korea."

The court order request was filed in the U.S. District Court for the District of Columbia.

Warmbier was ending a January 2016 visit to North Korea when authorities arrested him at the airport in the capital city of Pyongyang. He delivered a "confession" to stealing a poster from a hotel three weeks later. He was sentenced to 15 years at hard labor after being convicted in a show trial of crimes against the state in March 2016.

More:Otto Warmbier: How the family could collect on its $500 million judgment against North Korea.

There is "no mechanism" to compel North Korea to pay the Warmbiers, said Bruce McClure, the director of legal studies in political science and criminal justice at Northern Kentucky University in a Jan. 7 Enquirer article.