North Korea topped the agenda at the Diplomatic and Security Dialogue, which paired Tillerson and Mattis with Chinese State Councilor Yang Jiechi and General Fang Fenghui, chief of joint staff of the People's Liberation Army.
The Hamilton County Coroner's office did not perform an autopsy at the request of the Warmbier family.
After Warmbier had been released to the U.S.in a coma with severe brain damage last week, reports emerged that Warmbier traveled to Israel on a Birthright trip in 2014 and was an active member of UVA's campus Hillel.
Warmbier had tearfully confessed he tried to steal a propaganda banner and had been convicted of subversion.
Otto Warmbier arriving at a court for his trial in Pyongyang, March 16, 2015.
Otto Warmbier was returned by North Korea to the United States last week, more than a year after he had been sentenced to 15 years' hard labour.More news: Cristiano Ronaldo accused of tax fraud by Spanish state prosecutor
Warmbier's brother and sister spoke at Thursday's memorial, as did a number of his friends, said attendee Fred Koss.
Blue and white ribbons, the colours of Wyoming High School, were tied to the fence there.
Then, just before he was to be medically evacuated, the North Korean regime revealed that Warmbier had been in a coma for much of his imprisonment.
Warmbier died six days after he returned home.
"Unfortunately, the terrible torturous mistreatment our son received at the hands of the North Koreans ensured that no other outcome was possible", they said. After worldwide outrage and over a year of imprisonment, North Korea released Warmbier last week, saying his health had deteriorated after a bout of botulism.
"The family chose, rightfully so, not to share [his Jewishness] while he was in captivity... because they didn't want to embarrass [North Korea] by explaining that he actually was Jewish", said Mickey Bergman, one of the negotiators for Warmbier's release.
More than 2,500 family, friends and well-wishers gathered for his funeral in OH on Thursday.
Some 2,000 people filled an auditorium, cafeteria and gym at a school in Otto Warmbier's home town of Wyoming, Ohio, for the service. His family said it was told he had been in a coma since soon after his sentencing.