David C. Hennessy was born into an Irish Catholic family, son of Margaret and David Hennessy Sr., at 275 Girod St., New Orleans. David Sr. was a member of the First Louisiana Cavalry of the Union Army during the U.S. Civil War, formed after the state was occupied by Union troops. After the war, during the Reconstruction era, he served with the Metropolitan Police, a New Orleans force under the authority of the governor of Louisiana. Local white conservatives generally considered the Metropolitan Police as a form of occupation army, because it protected the right of freedmen to vote, in accordance with the Fifteenth Amendment. David Sr. was murdered in 1869 by Arthur Guerin, a fellow policeman. Young David was fatherless at the age of eleven.
Hennessy joined the New Orleans police force as a messenger in 1870. While only a teenager, he caught two adult thieves in the act, beat them with his bare hands, and dragged them to the police station. He made detective at the age of 20.
In 1882, Hennessy was tried for the murder of New Orleans Chief of Detectives Thomas Devereaux. At the time, both men were candidates for the position of chief. Hennessy argued self-defense and was found not guilty. Hennessy left the department afterwards and joined a private security firm given police powers by the city. He handled security for the New Orleans World Fair of 1884–1885. The New York Times noted that Hennessy's men were, "neatly uniformed and are a fine-looking and intelligent body of men, far superior to the regular city force."
In 1888, Joseph A. Shakspeare, the nominee of the Young Men's Democratic Association, was elected mayor of New Orleans with Republican support. Having promised to end police inefficiency, Shakspeare promptly appointed Hennessy as his police chief.
On the evening of October 15, 1890, Hennessy was shot by several gunmen as he walked home from work. Hennessy returned fire and chased his attackers before collapsing. When asked who had shot him, Hennessy reportedly whispered to Captain william O'Connor: "Dagoes." Hennessy was awake in the hospital for several hours after the shooting and spoke to friends but did not name the shooters. The next day, complications set in and he died.
Louisiana Songwriter Fred Bessel published a bestselling song about Hennessy in 1891, titled "The Hennessy Murder." It begins:
On November 24, 1893, John Williams, an African-American, was sentenced to life in prison for the rape of the 10-year-old, Rafael D'Amico. Williams was one of the state witnesses in the Hennessy murder trial. Ironically, Joseph Shakspeare had ordered the sentence. Hennessy is buried in Metairie Cemetery, New Orleans.
The lynchings were the subject of the 1999 HBO movie Vendetta, starring Christopher Walken. The movie is based on a 1977 book by Richard Gambino.
