The Tsialas family made a full-page ad in The Cornell Daily Sun, a student daily newspaper, on Monday and Tuesday asking students for help, family lawyer David Bianchi told CNN in an interview on Sunday.
There was no suspected fraud, Lombardi said. An autopsy is waiting, Bianchi said.
Honan said the authorities had received more than 150 leads. Several subpoenas have been issued, Honan said.
In his statement, President Pollack wrote, "Although we do not yet have a definitive answer about the cause of his death, it was widely known that an unregistered fraternity-sponsored event took place on October 24, that alcohol was served, and the first time it was served – years of students, including Mr. Tsialas, present. "
Pollack said that the events "unfortunately followed the pattern of wrong behavior in the Greek letter system." He said over the past two years, "many fraternities have been found to have been involved in violations during that time which were sufficient to suspend their recognition by the university."
In an e-mail on Sunday night, President of the Cornell Interfaith Council Cristian Gonzalez raised a question with Cornell University Police.
"We believe that it would be rude and wrong to celebrate this weekend given Antonio's death," Gonzalez said in a message on the paper later.
Bianchi said the last time Tsialas's mother saw him was when they had dinner on the night of October 24 at an off-campus restaurant. Ms. Tsialas visits the campus for the university's "Parents Weekend" and her father is scheduled to arrive the next day.
"What began as a beautiful weekend with our son Antonio turned into our worst nightmare," his mother, Flavia Tsialas, said in a recent Facebook post.
He remembers "she was very cheerful" when they met for dinner.
Bianchi said the Tsialas family "was very sad because this brotherhood would host a party that broke the rules." He suspected the fraternity served alcohol to first-year underage students.
"Antonio was drunk, left the program and then he disappeared and we don't know exactly how he died," Bianchi said. "We hope … that people will provide information starting that night."
Monica Haider and Darran Simon from CNN contributed to this report.