More than one person probably carried out the murders attributed to Jack the Ripper, a former detective has claimed.
Mr Marriott has spent a decade investigating Jack the Ripper
Former murder squad detective Trevor Marriott pointed to the "double event murders"- where both victims were found within 12 minutes of each other.
"It is highly unlikely that the murderer would have stopped a second time to murder a second victim in such a short space of time," he said.
Mr Marriott made the comments during a presentation in Londonderry on Monday.
He added: "My findings suggest that there may well have been two other similar
murders after the police closed their file."
Mr Marriott, who used to work for Bedfordshire police, has spent 10 years investigating the murders of five prostitutes in the Whitechapel area of London more than 100 years ago, attributed to Jack the Ripper.
In his speech, at the University of Ulster's Magee campus, he also questioned the feasibility of the majority of suspects named by Ripper enthusiasts over the years.
He said: "Most of the main suspects put forward aren't worthy of being classed as
"Some of them have been hyped up by publicity and media over the years
to suit their own means."
One such suspect was Francis Tumblety, a US "quack" doctor, arrested for gross indecency at the time of the murders.
He has been linked to the killings because he was alleged to have kept a collection of female organs.
A number of the Ripper victims were mutilated and had body parts
But Mr Marriott ruled him out on the basis of his known homosexual tendencies.
He said: "A lot of people would say that people who have such tendencies would
kill members of the same sex."
Mr Marriott also ruled out Queen Victoria's grandson, Prince Albert Victor - who was rumoured to have lived with his mistress in the East End.
He said: "It is highly unlikely that a member of the Royal Family and an heir to the
throne would be allowed to set up home in the East End of London.
"The other thing that rules the Duke of Clarence out is that the Royal Diary
shows that at the time of the murders he wasn't even in London. "
Mr Marriott said he did not have a prime suspect but that there were "other lines of inquiry" to pursue and he would love to solve the case.
"It would be one of the greatest breakthroughs in criminal history.
"But I am not setting myself on a pedestal and saying I am going to go out and solve it