A 17-year-old boy has been interviewed voluntarily over claims that he sexually assaulted a 15-year-old girl in a Chesterfield park.
An investigation is underway into claims that he assaulted the girl as they walked through Brearley Park, New Whittington.
Detectives want to trace two dog walkers - a man and a woman - who they believe may have seen or heard anything.
The incident happened just after midnight on the morning of Friday, December 15.
Witnesses or anyone with information should call DC Annetta Difelice at Derbyshire Police on 101, quoting reference 17000553019.
Crimestoppers can also be contacted on 0800 555 111