Jack and Patricia: the story of one woman and an obsession

In real life, Cornwell has attempted to emulate the efforts of her fictional heroine, with her determination to prove she has uncovered the identity of history's most notorious serial killer, Jack the Ripper. But, unlike Scarpetta, Cornwell's certainty she has found her man - in the figure of Victorian painter Walter Sickert - has only been greeted with widespread scepticism.

Now, undeterred by criticism of her book published in 2002, Portrait of a Killer, Cornwell has embarked on another mission to find further evidence for a new edition due next year. Assisted by a criminal psychologist and a forensic photographer, she has returned to London to examine fingerprints on some of the hundreds of letters sent to police at the time of the killings in 1888 claiming to be from Ripper to see if any match those of Sickert. Most of the Ripper letters are believed to be hoaxes.

Many believe that Cornwell's efforts are unlikely to bear further fruit. "She's acting the part of the fearless girl reporter, attempting to sort out what she probably sees as a great conspiracy of male incompetence that has been unable to solve the terrible murders of these poor women,'' said Matthew Sturgis, whose recent critically acclaimed biography of Sickert, six years in the making, comprehensively demolished the Ripper theory. "But in her desire to find answers, she simply hasn't followed very sound principles of investigation. It is a nonsensical misreading of the facts.''

Cornwell is clearly determined not to let go of the Sickert theory, about which she has said she is "100 per cent sure." The author herself was "on holiday" and not available for interview, but has been reported as saying: "I have never treated this is a book you walk away from. I am more certain than ever that Walter Sickert was the Ripper."

But in her pursuit of the Sickert theory, Cornwell is simply writing another chapter in a career in which the boundaries between her life and her fiction have become blurred. Born in Miami, she had a troubled childhood and moved to North Carolina with her mother. After graduating in English, she married her professor, Charles Cornwell and worked as a TV listings compiler on the Charlotte Observer, eventually becoming a reporter and moving to the crime desk, where she found her calling. But her first book, in 1983, was a biography of Ruth Bell Graham, the wife of the evangelist Billy Graham, a neighbour of her mother who acted as a mentor to the young Cornwell, encouraging her to take up writing as a career.

Determined to become a full-time crime writer, she left journalism and took a job in the medical examiner's office in Virginia as a technical writer, then a computer analyst; she also volunteered as a part-time police officer. But her first three novels were rejected.

But one editor suggested she expand the role of a minor character and in 1990 Postmortem was published, featuring Scarpetta and went on to win numerous awards. Twelve more books with Scarpetta as heroine in a style which has been described as "Hannibal Lecter-meets-Silent Witness" have followed; the next is due this autumn.

By the late 1990s she was earning multimillion-dollar advances, had three homes in parts of the United States, each with an identical office and separate computers for writing and research. But great success has also bought personal traumas. She has suffered bulimia and anorexia, been treated for alcoholism and was at the centre of a scandal after a lesbian affair with an FBI agent, who was involved in a shoot-out with her angry husband.

She is also said to be "difficult, driven and paranoid about security". The reason she has two computers in each office is said to be because of her fear that an internet virus will destroy her writings. She was searching for another case for Scarpetta when she became intrigued by the unsolved murders of Jack the Ripper, who mutilated five prostitutes in the East End of London in the summer and autumn of 1888. Instead of contriving the unlikely scenario on an American medical examiner investigating murders in Victorian London, she began a work of non-fiction, based on her belief that Sickert was the culprit.

Sickert followed the French Impressionist school and shared the liking of some of them for portraying urban scenes. He was particularly influenced by Degas, and in October, both artists will be included in major exhibition at Tate Britain, alongside that other chronicler of Parisien low-life, Toulouse Lautrec.

Some of his paintings were of murder scenes and he was known to be interested in the Ripper case. Cornwell spent $2m buying 32 Sickert paintings and the painter's desk to test for DNA; none was found, although suggestions that she had destroyed one painting in the process, which caused horror in the art world, were not proved true.

Undeterred, she paid for DNA tests on letters claiming to be from the Ripper; these were then compared with DNA samples from Sickert's correspondence, and similar sequences of mitochondrial DNA was found on the documents, the weakest kind of DNA link and equivalent to having a similar blood group. But as Steven Ryder, a Ripper expert, has said on the Casebook: Jack the Ripper website, not only were the documents contaminated by more than 100 years of handling, there was no proof Sickert licked his stamps and envelopes or that the Ripper letters were genuine.

The most the evidence could suggest was that "Sickert cannot be eliminated from suspicion of having written or hoaxed one or more Ripper letters". Evidence the paper used in both documents bore the same watermark was inconclusive. Cornwell also said Sickert had an abnormality of the penis, which rendered him impotent and therefore anti-women.

All of this is refuted by the facts, Sturgis says. "All the evidence suggests Sickert had an operation on the anus and while he had no acknowledged children, he was married three times and is known to have fathered at least one child out of marriage." Sturgis also points out it is well-documented that Sickert spent a large part of the period of the Ripper murders living in France.

Both the art world and Ripper enthusiasts continue to be bemused by her obsession. Richard Shone, editor of the Burlington Magazine and Sickert expert groans in horror. "She is obviously an extremely tenacious lady who does not want her extraordinary deductions to be contradicted by the evidence."

Trevor Marriot, a former detective and author of Jack The Ripper: The 21st Century Investigation, says: "She means well and understands the criminal world better than many armchair detectives. And we are all entitled to our beliefs. But at the end of the day, it comes down to the facts and you can't work on theory and wild speculation."

Who was the Ripper? Six theories

By Louise Cotton

FRANCIS TUMBLETY

He was investigated by Scotland Yard and was named in police reports as a suspect. Tumblety worked as a doctor in Canada and the US, although his credentials were questionable. In the 1860s, Tumblety came to England, where his homosexual activity landed him in trouble with the law. Tumblety was in London at the time of the Ripper murders. He had a profound hatred for women and was known to collect female wombs. The Ripper murders stopped after Tumblety fled England.

WILLIAM BURY

Bury, an alcoholic, was hanged for the murder of his prostitute wife, Ellen. In Mile End, where he lived, two knife attacks were committed on other women. Bury slept with a knife under his pillow and had worked as a butcher. He strangled his wife, but chopped up the body in a style similar to the Ripper's handiwork. He may have killed her because she knew too much. Some believe he could have been the Ripper or a copycat. He lived near the crime scenes and tried to flee Britain after the last murder.

GEORGE CHAPMAN

George Chapman, a hairdresser, was a strong suspect, fitting the description given by those who claimed they saw the Ripper. He had a homicidal streak and was accused of poisoning three women. He was hanged for one murder. He was single at the time of the Ripper murders and would have been able to roam at night. Though Chapman was known for poisoning women, he tried to kill his first wife with a knife.

THE DUKE OF CLARENCE

Prince Albert Victor, the grandson of Queen Victoria, was linked to the crimes in 1962. The claim was that syphilis had caused him to go insane and commit the murders. These accounts have been discredited, as Prince Albert was in Scotland at the time of two of the killings. Others have suggested that the murders were committed to prevent any "loose ends" involving an indiscretion by the Prince.

WALTER SICKERT

The artist is said to have confessed his part in the killings before his death in 1942. Patricia Cornwell claimed one "Ripper letter" bore the unusual watermark used on Sickert's writing-paper. The author believes his failure to procreate from his three marriages and numerous affairs turned him into a serial killer. She says pictures painted by Sickert in 1908 have an eerie similarity to autopsy pictures of Ripper's victims. But Cornwell failed to find DNA on Ripper letters held by Scotland Yard, to compare with samples from Sickert's desk and canvases.

JOHN PIZER

The Jewish shoemaker was the public's choice for fitting the Ripper profile. The killer was believed to be a butcher or craftsman who had access to sharp blades and wore a leather apron. Pizer fitted the profile, including the fact that he was often seen wearing such an apron, and was soon called "Leather Apron" in the media. He had convictions for stabbings and also had a known dislike for prostitutes. He fitted the stereotyped description of a short man with a dark beard, moustache, and foreign accent.