Essex Police are trying to identify a man who queued up at a post office and then threatened staff with a large kitchen knife.
The hooded man waited behind two customers at the post office in Thaxted near Stansted, before pulling out the long-bladed knife. He tried to rob staff but ran off empty-handed.
It happened at 1pm on Wednesday 21st of May.
The man was caught on CCTV and police are hopeful someone may recognise him or may have seen him near the post office last week.
Detective Sergeant Becky Young said: "We have carried out extensive enquiries but we have not been able to establish the identify of this man.
"There is no doubt that he is a dangerous person who is prepared to carry a long-bladed kitchen knife for use in a robbery and we want to catch him before he can attempt this sort of crime again."
Anyone with information is asked to contact police on 101 or call Crimestoppers anonymously on 0800 555111.
The Campaign to Protect Rural England has donated £1,000 towards the preservation of Thaxted Mill in Essex.
It was built in 1804 and was the largest and most advanced of all the Thaxted mills, it is the only one remaining.
By 1907, it was uneconomic to run and fell into disrepair.
In the1930s, it was renovated sufficiently to be used as a scout and youth centre.
It fell into dereliction again in the 1950s and remained so for 20 years until a Trust was formed to restore the building and open it to the public as a rural museum.
In 1991 the sails were re-erected and turned for the first time for 85 years.
Five years later, the stones were restored so that the mill could grind grain into flour once more.
An eleven-year-old boy has now died after a car crash in north Essex. The collision happened near Thaxted when the car he was a passenger in hit a tree on 3 October 2012.
It is thought the driver, a 19-year-old woman, had lost control of the vehicle. She is still in a stable condition at Addenbrooke's Hospital in Cambridge. An inquest into the boy's death is expected to open at the end of the week or at the start of next week.