On June 1, 1988 a child was sexually assaulted by a man while at home on the Fairfield estate, off Hook Road in Goole.
A 'significant development' in the investigation, which has never officially been closed, has now made officers believe the suspect could have been the boyfriend or friend of a teenage girl who babysat for families at the time.
The incident was reported to police in 1988 but the man was never identified at the time.
A statement from Humberside Police said: "Officers investigating the case are exploring extensive lines of enquiry and are now appealing to speak to anybody who would have been approximately 15-17 years of age at the time, who may have offered babysitting services in the area, to come forward."
Detective Sergeant Gemma Gallant added: “Our enquiries into this sexual assault have never stopped however, officers working on the investigation have made some significant developments in the case.
“Although this incident occurred some time ago I would appeal to any young women may have been in the company of a man, boyfriend, or partner and offering babysitting services at the time, or anyone who may have any information, no matter how small, to come forward as it may assist us with our enquiries.”
If you have any information that could assist with enquiries, please contact Humberside Police on 101 quoting investigation 16/55184/20. Alternatively you can all Crimestoppers anonymously on 0800 555 111