Four lorries were destroyed in an arson incident in Besthorpe earlier this month, igniting a Norfolk Constabulary appeal for witnesses.
The incident is reported to have taken place at approximately 9.30pm on Friday, March 3.
A number of small fires were deliberately started near to a line of tipper lorries on Bunwell Road, which then caused four of the vehicles to be engulfed in flames.
Norfolk Police wants to hear from anyone who may have witnessed any suspicious activity in the area around the time the incident occurred.
Officers are particularly keen to trace the driver of a silver vehicle who is believed to have been in the area at the time.
Anyone with information is urged to call PC Cherie Smith at Thetford Police Station on 101, or contact Crimestoppers anonymously on 0800 555111.