Three students at the University of Mississippi have been suspended by their fraternity, 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 that the photo was referred to campus police and the FBI, 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.

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

“The photo is inappropriate, insensitive, and unacceptable,” the fraternity chapter said. “It does not represent our chapter.”

William Lamar, the US attorney for the northern district of Mississippi, turned the photo over to the justice department’s civil rights division, according to the Mississippi Centre for Investigative Reporting, which first obtained and reported on the image.

The centre is part of the Local Reporting Network of ProPublica, a non-profit news organisation.

Mr Lamar did not respond to requests for comment on Thursday, and a justice department spokeswoman declined to comment.

Till who was 14 when he was killed in 1955, would have turned 78 on Thursday.

The sign, which has been replaced multiple times after being vandalised, marks the spot along the Tallahatchie River where Mr Emmett’s body was found after he was tortured and lynched.

He had been accused of whistling at a white woman behind the counter of the grocery store where he went to buy candy. Last year, the cold case was quietly reopened by the justice department after the woman recanted parts of her story.

“To me, that’s sacred ground,” Deborah Watts, Mr Emmett’s cousin and the co-founder of the Emmett Till Legacy Foundation, said in an interview on Thursday.

“Emmett’s body was dumped here. He was brutally murdered. He was lynched. What sense of pride does that represent for you?”

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The photo was posted to a private Instagram account in March and has since been deleted, according to the Mississippi Centre for Investigative Reporting.

The centre identified two of the students in the photo as Ben Leclere and John Lowe in a report published on Thursday.

Mr Leclere was holding a shotgun on the left side of the photo, and Mr Lowe was crouching down and did not appear to be holding anything, the report said. It did not identify the third student who was on the right and holding a rifle.

It was unclear if the bullet holes were made by the students or if they were remnants of previous vandalism.

Efforts to reach Mr Leclere and Mr Lowe on Thursday were unsuccessful. Phone messages left at their parents’ numbers were not immediately returned.

The Ole Miss chapter of Kappa Alpha, a national fraternity whose “spiritual founder” was Robert E Lee, the Confederate Civil War general, did not elaborate on the length or the nature of the suspensions. Neither did the national fraternity.

“We support the chapter and the actions they are taking,” the national Kappa Alpha order said through a spokesman.

Ole Miss defended its handling of the episode.

“This image and the actions portrayed in the photo of this off-campus incident are offensive and hurtful,” Mr Guajardo said on Thursday.

“While the image is offensive, it did not present a violation of university code of conduct. It occurred off campus and was not part of a university-affiliated event.

“We stand ready to assist the fraternity with educational opportunities for those members and the chapter.

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“The University of Mississippi will continue to build programmes that engage our students in deliberate, honest and candid conversations while making clear that we unequivocally reject attitudes that do not respect the dignity of each individual in our community.”

Ole Miss has previously grappled with controversial symbols of the state’s past.

In 2003, the Oxford, Mississippi, school retired its longtime sports mascot, Colonel Reb, a white-goateed, cane-toting Southern plantation owner that many had criticised as racist and anachronistic.

Mr Emmett’s family said on Thursday that their resolve was even stronger after the episode.

“This is still an open murder case,” Ms Watts said. “Damaging that sign is not going to deter me or other members of our family that are continuing to pursue justice.”

Ms Watts said she would leave it to law enforcement and prosecutors to determine whether a hate crime was committed by the three students in the photo.

“It’s like an assault on our humanity,” she said. “If somebody shot up Robert E Lee’s statue, what would they feel about it?”