Anthony Nazaire, a 19-year-old sophomore majoring in business administration from New York City, and his friend were stabbed early Sunday as several hundred people were leaving a fraternity-sponsored party at the Cornell student union, authorities said.
Police haven't said what touched off the melee.
Kiara Nazaire said she had spoken with her brother's friend and was told Anthony was trying to get him away from a confrontation when their assailant struck.
"He was defending his friend," she said, fighting back tears outside her family's apartment. "It wasn't to fight. He was pulling him away - and the coward just attacked them."
Nazaire said her brother had been visiting friends at Cornell and had developed an "upstate New York family" there.
She said her family went to Ithaca on Sunday but returned early Monday with little information from investigators about the progress of their investigation.
"I know the cops are going to do everything they have to do to make sure Anthony is at peace," she said. "We know justice is going to be served."
Police have not named any suspects in the stabbing. The attack followed a Saturday night party organized by Omega Psi Phi, a national fraternity of black men, at Willard Straight Hall as part of a series of events under the umbrella of Cornell's Black Students United group. Other "Say It Loud 2016" events included orientation sessions for incoming black students, ice cream socials, a Labor Day weekend barbecue and a game night. Investigators said they were interviewing witnesses and believe based on surveillance footage that some captured the killing on video.
VIDEO: Remembering Anthony Nazaire
Ithaca College President Tom Rochon said Anthony Nazaire graduated from Brooklyn Theatre Arts High School and was a member of the executive board of Brothers4Brothers, an Ithaca College student organization "dedicated to empowering men of color on our campus."
Kiara Nazaire said her brother wanted to be an entrepreneur.
"He wanted to be a black man with a bank," she said. "He wanted to get his hands on anything he could turn to gold."
Outside the student union Monday, Cornell senior Sonya Qamar said the killing was unsettling.
"There's the typical occasional break-in where a laptop is stolen or someone gets their wallet stolen out of the library, but it's completely different when it's someone getting stabbed outside one of your favorite libraries," the 21-year-old said.
Both schools said counseling would be available to students, faculty and staff.
Rochon said a campuswide gathering is scheduled for late Monday afternoon at the school's chapel.