A woman was robbed and sexually assaulted by a gang of three men as she walked through an underpass.
The 34-year-old was attacked in the tunnel under the Lawrence Hill roundabout in Bristol between 1700 BST and 1800 BST on Friday 17 September.
The three men snatched the woman's rucksack and handbag containing a quantity of cash.
Two of them then subjected her to a sexual assault while the other man watched.
The first man was aged about 19, 5ft 8ins tall, of mixed race and stocky build.
He had black hair and was wearing a dark jacket and dark trousers and had with him a dark-coloured bicycle with straight handlebars.
The second man was also aged about 19. He was 6ft tall, black and of slim build.
He had a shaved head and was wearing a dark waterproof waist-length jacket and black low-waisted jeans.
The third was aged about 19, black and of stocky build. He had short black hair and dark baggy clothing.
Police are appealing for anyone with information about the attack, or who recognises any of the descriptions, to contact them.