POLICE believe a man wanted in connection with the robbery of two women in 2011, who is believed to be from Nelson, recently returned to Manchester.
In both cases the man met women who were working as escorts and agreed a price for sex.
He handed over some cash and following sex threatened them and took back the money. In one instance he held a knife to the woman's throat.
The first incident happened on 30 April 2011 at an address on Commercial Street in the city centre involving a 26-year-old woman.
The second incident happened on 30 November 2011 at an address on Fernie Street and involved a 21-year-old woman.
Police believe the same man returned to Manchester recently.
On 3 January 2014, it is believed the same man met up two other women who were again working as escorts at addresses in the city on Little Peter Street and Chapel Street.
In one incident it is believed there was a dispute over money.
As part of an enquiry into the number passed to an agency in Manchester that was used by the man, police believe the same number has been used to contact a similar agency in Leeds.
Detective Constable Natalie McDonald, said: "Regardless of what you think about the circumstances surrounding these incidents, two young women have been threatened and robbed and in one case had a knife held to her throat.
"We think this man may be using escort services across the country and there are quite possibly other victims out there and the person responsible is clearly a danger to women.
"Now that he has stuck his head above the parapet after such a long period of time I want anyone with information about who he is to call me before any other women are subjected to similar incidents.
"The images are quite clear and we believe he has a fairly distinctive accent that one woman believed to originate from the Nelson area of Lancashire.
"If this information helps you identify him or you recognise someone from the images please do come forward.
"I would also urge women to be mindful of this man if they come across him not to engage with him but to leave where they are and contact the police."
Anyone with information is asked to call police on 0161 856 2510, or Crimestoppers, anonymously, on 0800 555 111.