A woman who has written anonymously to police alleging she has been raped is being urged to come forward.
In the letter to Avon and Somerset Police the woman says the rape took place in Taunton in 1968.
She said she had been walking home when she was offered a lift and was then taken to a quiet location and attacked.
The victim initially contacted the Crimestoppers charity in 2012 but at that time there was too little information for an investigation.
In December last year the woman wrote anonymously to Devon and Cornwall Police, again providing the basic circumstances of the assault and suggesting a man from Truro, Cornwall, was responsible.
The letter was passed to Avon and Somerset Police because the alleged offence happened in Taunton and an inquiry was launched.
Police said investigations are continuing and the man from Truro has been eliminated from inquiries.
Detective Inspector Becky Jarvis, from Taunton CID, said: "This woman has contacted us twice to tell us about the attack and we now need to speak to her to find out what more she can tell us.
"We have conducted inquiries to try and identify her with the little information we have but that has been unsuccessful.
"It is clear she is beginning to feel able to talk about the incident and I need her to contact us so that we can support her and investigate the attack.
"If you are the woman who wrote these letters, please get in touch with us. We will treat the information we get discreetly and with the utmost care - so please give us a call."