"I was left with a choice: I have got intelligent speculation, which I think is pretty long way down the track to proving that this guy was the Ripper. Do I include or exclude it?

"If I include it, it buggers up the book and people get excited for the wrong reasons. If I exclude it and a really sharp professional spots it ... I had to explore this possibility," he said, sitting in his tree-filled garden, about 3 miles from where Silver reigned, in a city still regarded as one of the most crime-ridden in the world.

The publicity around van Onselen's "The Fox and The Flies: The World of Joseph Silver, Racketeer and Psychopath", published in April, has made much of Silver being Jack the Ripper, the notorious Victorian serial killer who murdered at least five East London prostitutes in 1888.

But van Onselen, an acclaimed biographer who specializes in South Africa's criminal history and who took nearly three decades to research the book, only makes his Ripper case in the final 25th chapter, written in the last 36 months.

While the book has been well-received, reaction from "Ripperologists" has been skeptical as van Onselen makes his case on circumstantial evidence.

To his doubters the author said: "How many coincidences do you want to mount up in your mind simultaneously until you start saying this is a real possibility?"

Scores of people have been accused of the Ripper murders, but no one has ever been proven guilty and London police put the number of most likely suspects at just four, among them a poor Whitechapel resident named Kosminski who, like Silver, was a Polish Jew. At the time, Londoners speculated the killer was Jewish, leading to fears of an anti-Jewish backlash.

Van Onselen believes Silver fits the psychological profile of the Whitechapel murderer and he places his subject at the center of the scene of the Ripper murders. The evidence that Silver was in Whitechapel at the time of the Ripper murders includes the birth of his daughter there, van Onselen said.

As pimp and brothel keeper, Silver would have been familiar with the prostitutes working in the area, van Onselen said.

Silver, who was born in Poland, arrived in Johannesburg in 1898 fresh from a stint in Sing Sing for burglary and a stay in London a decade earlier. Shortly after arriving in Johannesburg, Silver set up a string of cafes, cigar shops and police-protected brothels.

Silver was litigious, wrote bold letters to newspapers and had an array of mocking aliases, van Onselen said. Jack the Ripper is believed to have taunted police with brazen letters to the papers.

Van Onselen, the son of a detective, tracked Silver across Africa, the Americas and Europe, "staggered by how mobile this guy was." In the end, Silver was executed as a spy in Poland in 1918.

Van Onselen points to similarities between the subject of his book and the Whitechapel murderer, both psychopaths with a deep hatred of women. Silver had bitter, violent relationships with women all his life.

"In terms of a template for this person, in terms of age, personality, mental illness, pattern for rest of life, this is the best fit there has ever been," he said.