(CNN) -- Days after the death of US student Otto Warmbier following 17 months detention in North Korea, the country's state media claimed his death was a "mystery."
Upon his return to the US, doctors who examined Warmbier said the former University of Virginia student had incurred significant brain damage and was in a state of "unresponsive wakefulness."
It's unclear how he came to be in that state.
The North Koreans had told US officials that Warmbier slipped in a coma after contracting botulism and taking a sleeping pill.
The 22-year-old's family alleges he was tortured.
"Unfortunately, the awful torturous mistreatment our son received at the hands of the North Koreans ensured that no other outcome was possible beyond the sad one we experienced today," said Fred Warmbier as he announced his son's death.
The KCNA news agency Friday said that Warmbier was treated in accordance with domestic law and said that allegations that he may have been tortured during nearly 18 months in detention were "groundless."
"The fact that Warmbier died suddenly in less than a week just after his return to the US in his normal state of health indicators is a mystery to us as well," state-run KCNA news reported.
Sentenced to hard labor
Warmbier was detained in North Korea in January 2016 at the airport in Pyongyang after a short tour of the country.
Two months later, he was found guilty of committing "hostile acts" against the North Korean regime and sentenced to 15 years hard labor in a trial that reportedly lasted about an hour.
Some of the proof used against him was purported security footage of him removing a political banner from his hotel.
More than a year went by without public word of Warmbier before the State Department learned of his dire condition on June 6. He was released a week later.
US President Donald Trump called the situation a "disgrace."
"He should have been brought home a long time ago," Trump said.
Warmbier died Monday, just days after he returned to the US, and his funeral was held in his hometown in Ohio Thursday.
Kenneth Bae, an American who was jailed for nearly two years in North Korea, told CNN he believed Warmbier could have been tortured, and cautioned other Americans against going to North Korea.