The killer, who began his attacks in August 1991, has claimed seven victims this year alone, the most recent in May. Most of the victims, five of whom were men, were strangled or suffocated.
The police, who have set up a task force with the FBI to track down the murderer, have suspected for about a year that there was a serial killer on the loose but only on Friday did they decide to make the announcement, when they appealed to the public for help.
Police said they had positively identified 18 of the victims but the names of the rest were unknown because the bodies were too badly decomposed.
The suspect has been identified in a police sketch as a large, muscular black man in his 30s. Richard Pennington, chief of the New Orleans police, said that a police officer was a suspect, but he refused to identify him.
The link to a police officer was made last April when Sharon Robinson, a casino coin-changer, and her friend, Karen Iverster, were murdered. Robinson's boyfriend was a police officer called Victor Grant, who has denied any wrongdoing.
Grant has not been charged and continues to carry out his desk job at the police department in New Orleans.
However, in the opinion of opponents of the death penalty, the most notorious serial killer in the United States is the state itself. More than two dozen people have been executed this year.
The latest execution occurred in the small hours of Friday in Oklahoma City. But there was a strange twist to the tale.
On Thursday night Robert Brecheen, the condemned man, was found in his cell suffering from a severe overdose of sedatives. Prison authorities rushed him to hospital where his stomach was pumped. After Brecheen had regained consciousness he was taken back to the state penitentiary, strapped to a bed and put to death by lethal injection.
"I suppose there is an irony to this," Jim Rabon, a spokesman for Oklahoma Department of Correction, said. "We have a responsibility for the health and welfare of our inmates, but we also have a responsibility to uphold the law."
Officials said the reason they had to revive Brecheen was that under a ruling made by the US Supreme Court in 1986, a condemned prisoner had to be aware of his execution and he had to know why he was being executed.
The execution was witnessed by the husband of a woman whom Brecheen murdered in 1983. Hilton Stubbs, 71, said he applauded the prison authorities' decision to bring his wife's murderer back to life before carrying out the sentence of death. "It wasn't his job to take his life," Mr Stubbs said.Reuse content