A wrongful death lawsuit filed this year by the parents of American college student Otto Warmbier against the North Korean government is now seeking more than $1 billion.

Fred and Cindy Warmbier, of Wyoming, Ohio, filed the suit in a federal court in Washington last April. North Korean authorities arrested their son in January 2016 for stealing a propaganda poster, and he was sentenced to 15 years in prison. He died last year after he was released from North Korea in a coma after 17 months of being tortured in captivity at a labor camp.

A motion filed in October in the lawsuit seeks $1.05 billion in punitive damages and about $46 million for the family's suffering, the Cincinnati Enquirer first reported.

North Korea has repeatedly denied the accusations that it tortured Warmbier, 22.

The Warmbiers' lawsuit claims that North Korea violated international law by forcing their son to confess to carrying out an act of subversion on behalf of the U.S. government.

The eye-popping figure sought in punitive damages is about 2.5 percent of North Korea's 2015 gross domestic product, according to the Enquirer. The amount aims to get North Korea to "change its unlawful behavior in the future," the motion says.

Wambier had traveled to North Korea with a tour group and was detained at the airport as they were preparing to leave.

In an emotional hearing this week in federal court in Washington, the Warmbiers said they wanted closure and justice for their son.

"We're here because we don't fear North Korea anymore," Fred Warmbier said Wednesday.

The bereaved parents told the court that they immediately became uneasy when they didn't hear from Warmbier after his trip to North Korea, and then described tense months of silence afterward. When a plane finally brought Warmbier home, the family expected a joyous reunion based on North Korea's claims that he was in good condition, claims that Fred Warmbier now calls "ridiculous."

His son was in a coma upon return, and died just days after coming home. President Donald Trump has credited a historic summit that he held in June with North Korean leader Kim Jong Un to Warmbier's death, saying it brought the two leaders together.

"Otto Warmbier is a very special person and he will be for a long time in my life. His parents are good friends of mine. I think without Otto, this would not have happened," Trump told reporters at the time.