Police want to speak to passengers who saw a woman being attacked and racially abused at a tram station.
The 22-year-old Asian woman was pinned against a wall and threatened with a knife by two men, who then spat in her face and threw one of her shoes onto the track.
The woman was attacked by the pair at the Trafford Bar tram station in Greater Manchester last Thursday.
Police said on Tuesday that it was "unbelievable" that no-one had come to her aid.
The woman was approached by the men on the Manchester-bound platform at about 1620 GMT.
Sergeant Alec McMurchy, from Greater Manchester Police, said: "This was a totally unprovoked assault which left the victim extremely traumatised.
"There were a number of people on the platform when this happened, including several workmen, but no-one came to this woman's assistance, and no-one has come forward as a witness which I find unbelievable.
"These people need to search their consciences and do the right thing by speaking to the police to help us find these two men."
One of the men was black, about 5ft 10ins tall and was wearing a black waist-length hooded jacket and black tracksuit bottoms.
His accomplice was also black, and in his early teens with dark brown or black hair which was cut short on the sides and on top. He was wearing a black scarf.
Anyone with information about the attack is urged to contact police, or Crimestoppers.