Three students at the University of Mississippi were suspended by their fraternity on Wednesday after an Instagram photo surfaced of them brandishing guns in front of a bullet-riddled memorial sign for Emmett Till, whose brutal murder in 1955 served as a catalyst for the civil rights movement.

The photo of the smiling Kappa Alpha members was the subject of a bias complaint filed with the university in March, according to Rod Guajardo, a spokesman for the university, which is commonly referred to as Ole Miss. He said he did not have a copy of the complaint and was unsure if it was a public record.

Mr. Guajardo said in an email on Thursday that the photo was referred to campus police and the F.B.I., which declined to investigate the matter further because it did not pose a specific threat. The university said it took no disciplinary action because, while offensive, what the students did was not a violation of the school’s code of conduct.

But the Ole Miss chapter of Kappa Alpha, which the three students are members of, said in a statement on Thursday that it took swift action after it learned of the photo on Tuesday.