The famous 'surgeon's photograph' of Nessie, later revealed to be a hoax
A police chief believed the existence of a Loch Ness monster was "beyond doubt", according to a historical document.
In 1938, the chief constable of Inverness-shire raised concerns about protecting Nessie from hunters.
In a letter he wrote: "That there is some strange creature in Loch Ness now seems beyond doubt."
The document has been released by the National Archives of Scotland (NAS) as part of an exhibition.
The government file reflects how ministers handled the issue of the existence of Nessie.
Reports of a monster in Loch Ness date back to 565 AD, when St Columba was said to have encountered a strange water beast.
But alleged sightings gathered pace in the 1930s, with a series of grainy photographs of the "monster" appearing in newspapers.
In 1933, the Scottish Office was asked to confirm the existence of a monster or sea serpent in Loch Ness.
A parliamentary question was tabled in the House of Commons asking whether, in the interests of science, an investigation would be launched into the creature's existence, but the question was ridiculed by the press at the time.
Ministers and civil servants were sceptical, but the documents show consideration was given to issues such as stationing observers round the loch to capture Nessie on camera and whether it would be possible to trap the monster without injury.
In the end it was felt that as the creature was popular with the public, it would be better not to kill either it or the myth.
However, this did not stop hunters from flocking to Loch Ness in the hope of capturing the monster.
The letter from William Fraser, the chief constable of Inverness-shire, to the Under Secretary of State at the Scottish Office, raises concern about the arrival of a hunting expedition in Fort Augustus in 1938.
It says they are "determined to catch the monster dead or alive".
The document goes on to describe how the party claimed they were having a special harpoon gun made and would return with 20 "experienced men" to track the monster down.
"That there is some strange creature in Loch Ness seems now beyond doubt, but that the police have any power to protect it is very doubtful," the letter concludes.
"If you have any suggestion to make or can offer any guidance in the matter, I shall be grateful."