A coroner's office in Ohio is investigating the death of a college student who died less than a week after his return to the US after nearly a year-and-a-half in North Korean detention.
A spokesman for Hamilton County Coroner Dr Lakshmi Sammaraco said the office "accepted the case" of Otto Warmbier, 22, who died on Monday in a Cincinnati hospital.
Mr Warmbier's parents did not state a specific cause of death, but cited "awful, torturous mistreatment" by North Korea.
Doctors had described Mr Warmbier's condition as a state of "unresponsive wakefulness" and said he suffered a "severe neurological injury" of unknown cause
He arrived in Ohio on June 13 after being held for more than 17 months.
The University of Virginia student was accused of trying to steal a propaganda banner while visiting with a tour group and was convicted of subversion.
He was put before North Korean officials and journalists for a televised "confession".
"I have made the worst mistake of my life," he said, choking up as he begged to be allowed to reunite with his parents and two younger siblings.
He was sentenced in March 2016 to 15 years in prison with hard labour.
His family said it was told he had been in a coma since soon after his sentencing.
Doctors said he suffered extensive loss of brain tissue and "profound weakness and contraction" of his muscles, arms and legs.
His eyes opened and blinked but without any sign that he understood verbal commands or his surroundings.
Unresponsive wakefulness is a new medical term for persistent vegetative state.
Patients in this condition who have survived a coma can open their eyes, but they do not respond to commands.
People can live in a state of unresponsive wakefulness for many years with the chances of recovery depending on the extent of the brain injury.
North Korea said Mr Warmbier went into a coma after contracting botulism and taking a sleeping pill.
Doctors in Cincinnati said they found no active sign of botulism or evidence of beatings.
In a White House statement, President Donald Trump said: "A lot of bad things happened, but at least we got him home to be with his parents."
He called North Korea a "brutal regime".
Mr Warmbier grew up in the Cincinnati suburb of Wyoming. He was salutatorian of his 2013 class at a highly rated high school and was on the football team.
Wyoming City Schools released a statement saying it was "deeply saddened" by his death.
"The countless contributions he made to his school and community through his leadership, actions, and limitless enthusiasm will be felt far into the future," the school district said.
Mr Warmbier's English teacher said he would be "dearly missed".
Mr Warmbier had planned to study in China in his third year of college and heard about Chinese travel companies offering trips to North Korea.
He was leaving North Korea on January 2 2016 when he was detained at the airport.
The organisers of Mr Warmbier's trip said they will no longer take US citizens to the country.
Young Pioneer Tours said on Facebook that his death shows that the risk American tourists face in visiting North Korea "has become too high".
The US department of state warns against travel to North Korea.
While nearly all Americans who have been there have left without incident, visitors can be seized and face lengthy incarceration for what might seem like minor infractions.
Jeffrey Fowle, also from Ohio, was detained in 2014 when he intentionally left a Bible in a nightclub.
Mr Fowle was freed after six months.
He said he was kept isolated most of the time but not physically abused.
He and others freed from North Korea have said they were coached and coerced into giving confessions.
Three Americans remain held in North Korea.
The US government accuses North Korea of using such detainees as political pawns.
North Korea accuses Washington and South Korea of sending spies to overthrow its government.