Hundreds of men have been asked for DNA samples to help police investigating the rape of a woman in Northants.
An 18-year-old woman was raped after being dragged into bushes in Abington Park on 5 February.
Forensic investigations have identified DNA traces from the rapist, but no match has been found on the millions of samples on the national database.
Samples from men who fit the offender's description and who work or live in the area of the attack are being contacted.
The officer leading the investigation, Det Ch Insp Tom Manson said that four men have already given samples to the enquiry team.
Suspect released
Det Ch Insp Manson said: "We have taken advantage of every forensic opportunity available to us in this case and that has fortunately identified the offender's DNA.
"I am convinced that the offender is local or knows this area well and so I am asking men to help us track him down by taking part in this simple procedure," he added.
The DNA sample is taken on a voluntary basis in the form of a mouth swab and will be tested at the Forensic Science Service in Birmingham.
The man involved in the attack is described as Asian and between 20 and 50 years old.
The 34-year-old Northampton man previously on police bail in relation to the offence has been released without charge.