Jewellery worth £35,000 was stolen from a jewellers in Gainsborough during a Christmas-lights switch on event in the town.
The theft took place at some point between 7.30pm and 8pm on Friday 18 November, when a diamond necklace and five diamond rings were stolen from Stanley Hunt Jewellers in Marshalls Yard while the store was open.
Lincolnshire Police said it would like to hear from anyone who may have been in the store at the time or in the area and saw anyone acting suspiciously.
Police are also seeking information from anyone who may have been offered any diamond jewellery for sale following the theft.
A person has been arrested in connection with this incident and has been bailed pending further enquiries.
The stolen items: