Relying on forensic science such as DNA testing and an image-enhancement computer, Cornwell argues in her new book, "Portrait of a Killer: Jack the Ripper Case Closed," that Jack the Ripper could have been Walter Sickert, a painter and printmaker who was an important British impressionists.
An examination of DNA samples from letters, envelops and stamps reportedly sent by Jack the Ripper to the Metropolitan Police, and by Sickert, his first wife and others helped Cornwell reach her conclusion.
"At best, we have a 'cautious indicator' that Sickert and Ripper mitochondrial DNA sequences may have come from the same person," Cornwell writes in the new book published by G.P. Putnam's Sons.
The real proof may never be available because Sickert was cremated, leaving no evidence of his DNA behind.
"Walter Sickert was a forensic scientist's worst adversary," Cornwell writes. "He was like a twister tearing through a lab.
"He created investigative chaos with his baffling varieties of papers, pens, paints, postmarks, and disguised handwritings, and by his constant moving about without leaving a trail through diaries, calendars, or dates on most of his letters and work."
The author worked with Paul Ferrara, director of the Virginia Institute of Forensic Science and Medicine, who used a forensic image-enhancement computer to compare watermarks on stationary that Jack the Ripper and Sickert apparently had used.
Cornwell also studied Sickert's art work, searching for signs of the kind of morbidity, violence and hatred of women that someone like Jack the Ripper would have possessed. For example, she says in the book that Sickert's sketch, "He Killed His Father in a Fight," mirrors the murder scene of a Ripper victim, Mary Kelly.