Officers investigating the murder of Derbyshire economics graduate Jia Ashton say they have forensic evidence to link the killer to the murder scene.
The body of the 25-year-old woman was found on 13 March in Sleetmoor Woods near Somercotes. She had suffered head injuries.
Derbyshire Police has also issued CCTV images of a man seen in the area on the evening Mrs Ashton died.
Det Ch Supt Steve Cotterill said the man may be able to help with inquiries.
"Jia had trauma to her head and face and detailed forensic analysis of the scene has produced evidence about her killer", said Det Ch Supt Cotterill.
"We now have forensic evidence that will help us trace the person responsible for her death.
"Early indications suggest that the murderer is not on any police database and has not been any part of the police inquiry so far.
"The new evidence will help us eliminate innocent people from the investigation and will help us identify the killer."
Police are concentrating their investigation on a man seen in the woods who they have not yet traced.
He is described as dressed entirely in green with a dark green beanie hat, a thigh-length green waterproof walking jacket and dark green or brown combat trousers.
He was about 6ft tall, of athletic build, between 45 and 55 years old and with blond or mousey stubble on his chin.
The man was seen acting suspiciously in the woods and jumped into the undergrowth when seen by others, police said.
A Facebook page on the murder investigation has been seen by more than 400,000 people.
A reward of up to £20,000 has been offered to help find her killer.
There was no evidence a weapon had been used in the attack and there was no apparent sexual assault, police said.