Until now, the Ripper was believed to have restricted his activities to the foggy streets of Whitechapel, in the East End.
A retired police officer has uncovered documents which connect the Ripper to the killing of Percy Knight Searle, nine, who was found stabbed to death in Havant, Hampshire in 1888 - the year of the Whitechapel killings - while on an errand for his mother.
Gavin Maidment, senior assistant at Havant Museum, has discovered archives which mention that a magistrate received a letter bearing a Portsmouth postmark, days before Percy's killing, signed "Yours, Jack the Ripper."
The letter told police not to bother looking for him in London because "I'm not there", suggesting he had moved his activities to the south coast.
During the Ripper's reign of terror, the police received many letters claiming to be from him. Most were disregarded as having been sent by cranks. The Portsmouth letter was taken seriously at the time.
Robert Husband, 11, the only witness to the killing, said in a statement that he saw a man stab Percy. Husband himself was eventually charged with the murder after a pocket knife found at the scene, believed to be the murder weapon, was found to belong to his brother. He was acquitted at Winchester assizes and the case remained unsolved.
Mr Maidment, a policeman for 30 years, is now trying to trace descendants of the two boys and of members of the jury. He intends to write a book about the case.
"It was the newspaper reports of the time which got me hooked," he said. "The case throws up fascinating facts about society at the time. I'm amazed that this case has not received more publicity over the years and so little is known about it. The Ripper link may be a red herring, but it is possible that he did kill outside London as the letter suggests. It will be interesting to talk to any descendants of those involved in the case to find out what they have been told."
Mr Maidment admits that it is difficult to discover whether the Ripper had any links with the area because his identity has never been proven.
One theory is that the Ripper was the brother of Michael Maybrick, the mayor of Ryde on the Isle of Wight between 1900 and 1911.
James Maybrick was a womanising Liverpool cotton broker who was also a drug addict and a frequenter of London brothels.
Another theory was that the serial killer was Robert D'Onston Stephenson, a journalist living in the East End. The former soldier and black magician is believed to have spent eight months in Portsmouth shortly after the murders in 1888. Queen Victoria's grandson, the Duke of Clarence, was also suspected after syphilis affected his sanity.
"The trouble is no one knows for sure who the Ripper was," said Mr Maidment. "That will probably always remain a mystery."