Police want to trace two men who were drinking with a man who is suspected of sexually assaulting an American student in Edinburgh.
The 22-year-old, who is studying in the capital, said she was attacked between 0400 BST and 0430 BST on Monday in Barrie's Close, near Parliament Square.
The woman had been drinking with friends in Niddry Street before visiting the Cowgate's Opium nightclub.
Officers think the attacker and his group had befriended the woman's group.
The two men who were drinking with the suspect were both thought to be Scottish.
The first man is white, 20 to 25 years old, between 5ft 9in and 5ft 10in tall, of average build, with light brown collar-length hair and a spotted complexion.
He was wearing a white short-sleeved shirt.
The second man is white, 20 to 25 years old, between 5ft 7in and 5ft 8in tall, of medium athletic build, with short, light brown hair and facial hair.
He was wearing a blue short-sleeved shirt with white vertical stripes.
Det Insp Scott Cunningham, of Lothian and Borders Police, said: "We do not believe that these men are suspects or had anything to do with the assault.
"However, we are certain that they know the man responsible and may be able to assist us in locating him.
"We would urge these men to come forward and speak to police immediately.
"Similarly, anyone who remembers seeing the group, either in Opium or around the Cowgate and has information that can help our investigation, is asked to come forward at once."