An anonymous letter could be the key to solving the case of a nine-year-old girl who vanished without a trace in Scunthorpe 33 years ago.
Christine Markham went missing on her way to school in 1973. Police searched 5,000 homes but she was never found.
The letter, which police said included information which could be helpful to the inquiry, was sent to Scunthorpe’s Major Investigation Team last month.
Detectives appealed for whoever wrote it to contact them in confidence.
Christine’s family have been told about the letter, which was addressed to Det Sgt Craig Scott.
He said: “I would like to thank the person for the letter they have sent to me but it is really important that I speak to them personally.
“I wish to reassure them that all information they give me will be treated with sensitivity and they can contact me in confidence.”
Earlier this year, Humberside Police announced it was carrying out a review of the case, and that details of the investigation were being transferred from a paper system into the Holmes (Home Office Major Enquiry System) computer.
Before she disappeared Christine walked part-way to school with two of her siblings, who then caught a bus to another school they attended.
They said that through the bus window, they saw Christine turn around and walk back in the direction in which they came.
She had been known to take the odd day off school and wander the area.
That night, police and around 60 volunteers conducted an extensive search of the area.
A number of sightings were reported to the police of Christine’s whereabouts and about 2,000 witness statements were recorded during the inquiry.
Detectives said that Christine was still classed as a missing person but was presumed dead.
DNA has been taken from Christine’s family to help officers identify her if she should ever be found.