A woman walking through Northampton’s Racecourse late at night was pushed to the floor and sexually assaulted.
The attack happened sometime between 10.30pm and 11pm on Friday March 21.
A police spokesman said: “The woman was walking on the path between Brick Lane and Military Road when she was grabbed from behind and pushed to the floor by a man.
“As she shouted for help, a young man went to her assistance and the attacker fled.
“The attacker was black and about 6ft. He was wearing dark clothing, including a fitted jacket which was quite short.”
Officers investigating the assault are particularly keen to speak to the stranger who went to help the woman. He was mixed-race, between 20 and 24 years old and wore a dark jacket and lighter coloured trousers.
After helping to scare off the attacker, he walked with the woman to the edge of the Racecourse.
Witnesses to this assault, or anyone with any information about it, can call the police on 101 or Crimestoppers anonymously on 0800 555 111.