WASHINGTON (WASHINGTON POST) - In June last year, a plane touched down at a tiny airport in Cincinnati, and Mr Fred Warmbier and his wife Cindy boarded before medical personnel carried their son Otto off the plane and onto a stretcher.

The 22-year-old - an athletic, intellectual and charismatic University of Virginia student - was in a coma.

The Warmbiers spent the next several days at a hospital with their son before he died.

Since those days, Mr Otto Warmbier has been a searing, painful symbol of North Korea's cruelty: a young American with the brightest of futures, held against his will for nearly a year and a half.

A year later, President Donald Trump was praising North Korean leader Kim Jong Un at a historic summit in Singapore, saying he had a "great personality", that the two men had a "very special bond", and promising that the nuclear threat from that country had ended.

Mr Trump told reporters that the summit would not have happened were it not for Mr Otto Warmbier.

"Something happened from that day. It was a terrible thing. It was brutal. But a lot of people started to focus on what was going on, including North Korea," Mr Trump said. "I really think that Otto is someone who did not die in vain."

The Warmbier family responded with a few words.

"We appreciate President Trump's recent comments about our family," Mr Fred Warmbier and Mrs Cindy Warmbier said in a statement. "We are proud of Otto and miss him. Hopefully something positive can come from this."

Their lawsuit against North Korea - which alleges the Warmbier's son was "brutally tortured and murdered" by the "criminal" regime - proceeds.

"The summit doesn't affect what we're doing at all," said Mr Richard Cullen, the Warmbier's attorney on the case. "We're moving full speed ahead. They're looking forward to their day in court, where they can prove that Otto's death was the result of his brutal treatment at the hands of the North Koreans."

Normally, US citizens cannot sue foreign countries, but after Mr Trump and the State Department put North Korea on the list of state sponsors of terrorism in the fall, the Warmbiers were able to file their legal challenge.

The lawsuit has been filed, translated and is on its way to North Korea, where it will be hand-delivered, Mr Cullen said.

Mr Otto Warmbier had visited North Korea with a tour group on his way to a study-abroad programme in Hong Kong when he was detained at the airport in Pyongyang in January 2016.

He did not have contact with the outside world after a sham trial that March. US officials demanded his release after nearly 18 months, and he was medically evacuated.

He was brain dead and unresponsive when his family finally saw him again.

Their public comments have been few, but the central theme has been consistent: They miss Otto.

"Obviously, this has been an unimaginable, painful, horrific experience, and they feel very strongly that the North Korean regime should be held accountable for the death of their boy," said Mr Cullen.

"They feel there's no better venue for that than a United States court."