A woman who could be a vital witness to a sex attack in Staines is being sought by Surrey Police.
Detectives have issued CCTV images of the woman, who officers believe could have important information.
Det Sgt Sean Kelly said: "We believe this woman may be a key witness without realising it."
A 31-year-old woman was assaulted on the humpback bridge in Kingston Road on 27 March in what police have called an "extremely distressing attack".
Det Sgt Kelly urged the woman to contact police as soon as possible, even if she thought she did not have any relevant information.
He also urged anyone who recognised her to get in touch with the force.
In the incident earlier this year, the victim was approached by a man who tried to talk to her. He then pushed her against a wall and indecently assaulted her.
The woman was able to escape after hitting the man and forcing him away at about 0100 GMT.
She was uninjured, but police said it was being dealt with a serious incident.
The man was described as black, aged about 25, with dark hair in a crew cut. He was about 5ft 6in (1.67m) tall.