They say officers are now in a position to update the description of the man after trawling through hours CCTV footage.
Detective Inspector Zoe McKee said: “A woman in her early twenties was subjected to a serious sexual assault as she waited for a friend on Rosemary Street at around 3:30am last Thursday.
“The attack was a horrific experience for this young woman and we are working hard to arrest the man responsible.
“I would ask that the public support our investigation, specifically in identifying a man we would like to speak with in connection with the sexual assault.
“He is a black man, of slim build and somewhere between 5’6” and 5’10” in height. At the time of the incident, he was wearing dark coloured jeans and shoes.
“He was wearing a dark short sleeved top with a thick white band at the bottom. The t-shirt brand is thought to be “Supply and Demand” with a triangular design at the back nape of the neck.
“He was also wearing a dark coloured baseball cap with a silver rim and white lettering on the front.
DI McKee added: “If you can help us identify this man please call the Rape Crime Unit on the non-emergency number 101. Or, you can contact Crimestoppers on 0800 555 111.”