Officials at the University of Cincinnati Medical Center, where he was treated, declined to provide details, and Warmbier's family on Tuesday asked that the Hamilton County Coroner not perform an autopsy.
U.S. President Donald Trump blamed "the brutality of the North Korean regime" for Warmbier's death and South Korean President Moon Jae-in, who had advocated dialogue with the North, said Pyongyang had a "heavy responsibility" in the events leading up to the American's death.
Otto Frederick Warmbier, a University of Virginia student, attends a news conference in Pyongyang, North Korea, on February 29, 2016.
Warmbier died Monday after being released last week from North Korea, where he had been held for about 17 months. North Korean officials originally claimed that Otto had become ill from botulism after his March trial and slipped into a coma after taking a sleeping pill.
The funeral for Otto Warmbier, 22, took place at his hometown high school, Wyoming High, in Cincinnati.
"The United States once again condemns the brutality of the North Korean regime as we mourn its latest victim". He had been accused of stealing a propaganda poster and was serving a sentence of hard labor.
U.S. doctors say there is no evidence he suffered from botulism, and the Warmbier family believe he died as a result of "awful torturous mistreatment".
A negotiator involved in Warmbier's release said his Jewishness was hidden as a tactic because he was accused by Pyongyang of acting on behalf of the United Methodist Church. His family blames the North Korean authorities for his death.
It was unclear whether Trump's remark represented a shift in USA policy toward China or he was simply expressing frustration with North Korea.
Fred and Cindy Warmbier watch as their son is placed in a hearse after his funeral on Thursday..
"Our relevant agencies treat all criminals. thoroughly in accordance with domestic laws and worldwide standards and Warmbier was not an exception", a spokesman for the National Reconciliation Council said.
Warmbier's brother, sister and friends all spoke at a public funeral Thursday morning at Wyoming High School.
"Kim Jong-un and his ilk have repeatedly assassinated family members and dissenters, violated nuclear weapons agreements, and held an entire nation hostage for far too long", Garrett said.