Officers are trying to trace a woman who spoke with a rape victim after the attack in Glasgow.
The 21-year-old woman suffered a serious sexual assault in the vicinity of Sauchiehall Street and Sauchiehall Lane just after midnight on Wednesday June 9.
Police Scotland are now seeking a woman who spoke with the victim outside the Boots store at the Charing Cross end of Sauchiehall Street, near Glasgow Dental Hospital.
They spoke for a period of around 15 minutes, at about 12.30am.
Detective Inspector Stella McCulloch, from the National Rape Taskforce, said: “Our inquiries remain ongoing into this very serious incident and as part of this we are especially keen to trace this woman.
“We believe she spoke to the victim in the doorway of the Sauchiehall Street Boots store and offered her assistance.
“I believe she may have information that is vital to our inquiry and would appeal to her to come forward.
“Despite the time of night, we do know the city centre area was reasonably busy with passing traffic and pedestrians.
“Anyone who may have seen the interaction between these two women in Sauchiehall Street, or either the witness or victim around the time of the incident, is asked to contact officers to help our inquiry.”
The woman is described as being aged between 30 and 40, with shoulder-length, reddish-blonde hair.
She was wearing an orange or rust-coloured jumper, black three-quarter length trousers, purple socks and black trainers.
Police Scotland said she was carrying a dark-coloured rucksack over both shoulders and also a white shoulder bag with the word “Castle” printed on it.
The suspect for the attack is a man who is 5ft 7in, of medium build, and aged in his 30s or 40s.
He had dark facial stubble and was wearing dark-coloured clothing.