SEOUL, South Korea (AP) — The parents of a former U.S. hostage who died after being released from North Korea in a coma in 2017 say they are committed to finding and shutting down illicit North Korean business assets around the world in efforts to hold its government accountable for widespread human rights abuses.

In a news conference in Seoul on Friday, Fred and Cindy Warmbier called for the Trump administration to raise North Korea’s human rights problems as it engages in negotiations to defuse the country’s nuclear threat.

“My mission would be to hold North Korea responsible, to recover and discover their assets around the world,” said Fred Warmbier, who was invited to a forum hosted by a Seoul-based group representing the families of South Koreans abducted by the North during the 1950-53 Korean War.

“We feel that if you force North Korea to engage the world in a legal standpoint, then they will have to ultimately have a dialogue. They are not going to come and have a dialogue with us any other way,” he said.

The Warmbiers have claimed that their college student son, Otto, was tortured by North Korea after being convicted in 2016 of trying to steal a propaganda poster and imprisoned for months.

The 22-year-old suffered severe brain damage and died shortly after being returned to the United States in a vegetative state in June 2017.

The North denied that it tortured or cruelly treated the University of Virginia student and accused Washington and Seoul of a smear campaign.

In December last year, a U.S. federal judge ordered North Korea pay more than $500 million in a wrongful death suit filed by the Warmbiers over their son, although they are unlikely to collect on the judgment.

The Warmbiers are also pushing legal action seeking the closure of a hostel operated on the grounds of the North Korean embassy in Berlin and plan to go after other hostels the North operates in Europe.