Otto Warmbier, an American student detained in North Korea for committing “hostile acts” has died, his parents confirmed Tuesday in a statement. He was 22.

Warmbier, who returned to America last Tuesday, having previously been sentenced to 15 years hard labor after stealing pro-government paraphernalia from his hotel, had lapsed into a coma before his return. The North Korean government claimed Warmbier had contracted botulism shortly after his conviction of crimes against the communist state in March 2016.

Doctors treating Warmbier upon his return to Ohio stated, however, that they found no evidence of botulism, instead finding “extensive brain damage.” The North Korean government has not remarked on the discrepancy or provided any explanation for what could have caused Warmbier such brain damage in prison.

“It is our sad duty to report that our son, Otto Warmbier, has completed his journey home,” his family wrote in a statement.

“We would like to thank the wonderful professionals at Cincinnati Medical Center who did everything they could for Otto. Unfortunately, the awful torturous treatment our son received at the hands of the North Koreans ensured no other outcome was possible beyond the sad one we experienced today.”

Otto Warmbier, 22-year-old US student detained in North Korea, dies after returning home in coma pic.twitter.com/SONqyO3Voq — Jason Calabretta (@JasonCalabretta) June 19, 2017

According to the Warmbier family, Otto was “unable to speak, unable to see and unable to react to verbal commands.”

Warmbier had gone to North Korea in early 2016 on an adventure tour of the rogue state, under the auspices of the China-based Young Pioneer Tours, which preys on the curiosity of young westerners by offering “Budget tours to destinations your mother wants you to stay away from!”

Warmbier was arrested during his visit for allegedly having attempted to steal a communist propaganda sign and forced to confess to the “serious crime” on North Korean television in February 2016. Warmbier pleaded guilty to taking down a political sign from a staff-only area of his hotel. “I have made the worst mistake of my life, but please act to save me,” he said at the time.

Under duress, Warmbier accused the United States of bribing him to steal the sign, calling it “the worst mistake of my life.” In an appearance carefully choreographed by North Korean authorities, Warmbier said that although his crime was “very severe and pre-planned,” he was grateful for the regime’s “humanitarian treatment of severe criminals.”

Warmbier was sentenced to 15 years hard labor for his “crime.”

North Korea continues to imprison three other U.S. citizens: academics Kim Hak-Song and Tony Kim, and businessman Kim Dong-Chul.

Update: President Donald Trump has released a statement on Warmbier’s passing: