New Orleans is expected to apologise for the worst mass lynching in United States history resulting in the killing of 11 Italian immigrants in the Louisiana city.

Mayor LaToya Cantrell will deliver the formal apology and has appointed Vincenzo Pasquantonio, the head of the city’s Human Relations Commission, as the liaison.

A proclamation is due to be released on April 12. The official declaration will be delivered at the American Italian Cultural Centre in New Orleans.

“This has been a longstanding wound,” Michael Santo, a member of the Order Sons and Daughters of Italy, the organisation that requested the apology earlier this year, told the Guardian.

The horrific lynching incident took place in 1891. It took place after a group of Italians accused of murdering a police chief were acquitted.

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David Hennessy, the police chief, was attacked by four men nearby his residence on October 15, 1890. When he died, he reportedly blamed Italians for his death.

At that time, about 30,000 Italian immigrants were living in New Orleans. Following Mr Hennessy’s murder investigations, hundreds of Italian immigrants were arrested and interrogated. Nineteen of them were indicted. Nine faced trial, resulting in the acquittal of six and a hung jury for the remaining three.

After the verdict on the death of Mr Hennessy, a group called the “Vigilance Committee” was formed. The group placed ads in morning newspapers calling on community members to be “prepared for action.”

The Times-Picayune of New Orleans reported in 1991 that a mob of thousands of people gathered at the statue of Henry Clay before storming into the jail where 11 of the men accused of killing Mr Hennessy were attacked.

The jailers opened the cell door detaining the 11 men and told them to run. Nine of those men were fatally shot. Two other men were hanged. Eight of the men killed were US citizens and three other were Italian citizens.

The mass killing resulted in Italy temporarily closing its embassy in the United States. The US embassy also closed in Italy in reciprocation.

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The year after, in 1892, the US government paid $25,000 to the victims’ families as reparations.

It “was a horrific act of collective violence inspired by ethnic prejudice, and it has a claim to constituting the largest mass lynching in US history, but it was hardly the largest act of collective violence in US history or even Louisiana history,” historian Michael J. Pfeifer, said in his book detailing the history of lynching and its root in the US, the Guardian reported.