Mr Marriott has spent a decade investigating Jack the Ripper
Jack the Ripper may have killed his first victim 25 years earlier than previously thought, a retired murder detective has claimed in a new book.
It is thought that Jack the Ripper killed and mutilated at least five prostitutes in the East End between August and November 1888.
But Trevor Marriott says he may have struck in 1863 and 1872.
Mr Marriott will be presenting his findings at the Docklands Museum which is hosting an exhibition on the killer.
The body of 28-year-old prostitute Emma Jackson was found in a brothel in St Giles, central London, in April 1863.
She had five wounds to the throat and had not been robbed. The case was never solved.
Mr Marriott also uncovered a second case he believes may have been committed by the Ripper.
Nine years after the Jackson murder, on Christmas Day 1872, Harriet Buswell was found with her throat slit at her lodgings in nearby Great Coram Street, after returning home the previous evening with a male guest.
Both cases remain unsolved.
In his book, The Evil Within, Mr Marriott claims that Jack the Ripper did not remove internal organs from two of his victims.
Traditionally, the serial killer is alleged to have removed organs from the bodies of his victims, including his second "official" victim Annie Chapman and Catherine Eddowes, his fourth, with a degree of medical precision.
But Mr Marriott said: "The organs were not removed by the killer at the crime scenes but by person or persons unknown for medical research at some point between the bodies being removed from the crime scenes and the post mortems taking place some 12 hours later.
"In both these cases the bodies had been left alone and unattended outside makeshift mortuaries."