(CNN) The largest mass lynching in US history killed 11 Italians in New Orleans in 1891. And now an Italian-American group says the city's mayor is set to offer a first-ever apology to Italian-Americans for the city's role in the lawless murders.

At the time, the city was grappling with the murder of its popular police Commissioner David Hennessy, and during a period of anti-immigrant sentiment, fingers pointed toward darker-skinned Italians new to the city. Police rounded up more than a dozen Italians in the wake of Hennessy's death.

But when the jury acquitted them of the killing, tensions ran high. Many demanded blood

According to a story published in the Washington Post, on March 14, 1891, a crowd of 8,000 assembled on New Orleans' Canal Street, "almost filling up the large space from curb to curb on each side of the boulevard." The crowd, possessed by an "ungovernable" fury, had guns and arrived at the parish prison at 10:30 that night. Prison guards let the mob into the prison, where they eventually found the Italian prisoners. "The shotguns belched forth and the slayers of Hennessy fell dead in their tracks," the story says.

They left the bodies "riddled by bullets or hanged to lamp posts," the Post reported.

New Orleans Mayor LaToya Cantrell is set to issue an apology, according to the Order Sons and Daughters of Italy in America.

CNN reached out to Cantrell's office, but a spokeswoman for the mayor wouldn't comment on whether Cantrell would issue a proclamation, or when it would take place.

An artist's sketch depicts the mob that gathered in New Orleans in 1891 to "avenge" the police commissioner's murder.

Undoing hurt

The OSDIA Commission for Social Justice said it expects Cantrell to present the "Official Proclamation of Apology" in a ceremony on the morning of April 12 at the city's American Italian Cultural Center.

Mike Santo, who serves as special counsel for the commission, said he'd become aware of the lynching a few years ago, realizing how the 1891 lynching was a "longstanding wound" for the Italian-American community.

He said the commission got in touch with the mayor, who was amenable to the proposal, and his group has been coordinating for weeks with a liaison in the mayor's office to get the proclamation written.

He praised Cantrell, calling her the "right woman at the right time" to step up and acknowledge a darker aspect of her city's history.

"It takes a lot of nerve to do that," Santo said. "People want to see that, especially today."

He said he personally felt the pending proclamation was "refreshing." On behalf of Italian-Americans more broadly, he said, "Thank you, thank you, thank you."

A dark moment in history

Italians were regular victims of nativist hostility in the 1890s, and more than 20 were lynched in episodes around the country throughout the decade. The HBO movie " Vendetta ," starring Christopher Walken, released in 1999, tells the story of the New Orleans lynching, and is based on a book of the same name.

The Washington Post pegged the commissioner's murder on the Mafia, a concept then only just dawning on the American consciousness.

And The New York Times ran an editorial showcasing the extreme anti-Italian sentiment in the country at the time: "These sneaking and cowardly Sicilians, the descendants of bandits and assassins, who have transported to this country the lawless passions, the cut-throat practices, and the oath-bound societies of their native country, are to us a pest without mitigations."

Conversely, The Post characterized the mob as composed of "cool-headed men, lawyers, doctors, merchants, and political leaders, all person of influence and social standing."

But it wasn't just powerful figures in New Orleans who cheered the lynching. A decade before he would assume the presidency, Theodore Roosevelt wrote of a discussion about the lynching at a dinner he attended, where Italians were present. "Personally I think it is rather a good thing, and said so," he told his sister in a letter.

Santo, the special counsel for the Italian-American group, said it's "very easy to walk away from a problem," but that it was refreshing to see this history acknowledged.