Detectives are trying to contact the writer of a letter sent to Downham Market police station.
They say that the hand-written letter, which was received just before Christmas, contained 'useful information' about a criminal offence, which officers are very keen to follow up.
But the sender did not include their details with the note, which arrived on December 19. Therefore officers have been unable to contact them to find out more details, in order to move their investigations forward.
A Norfolk police spokesman said officers still hoped that the letter writer would get in touch.
She added: 'The letter writer provided some useful information about a suspected criminal offence however we are keen to develop this further and would urge them to contact Detective Sergeant Andy Hill on 101 as they could hold further information which could assist our enquiries.'
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