A recently discovered letter written in the blood of notorious Edinburgh murderer William Burke is going on display to the public for the first time.

The gruesome document was unearthed in a scrapbook which was compiled in the wake of the infamous 19th century Burke and Hare bodysnatcher murders.

The bizarre letter simply states that the text is written in blood taken from the head of Burke after he was hanged in Edinburgh on 28 January 1829.

The letter will go on display later this month for an University of Edinburgh event which is being held as part of the Scotland-wide annual Festival of Museums.

A newly-discovered petition which was signed by hundreds of medical students at the city's university just before the Burke and Hare murders - in which they complained of a lack of bodies to practice on - will also be unveiled for the first time.

Joseph Marshall, head of special collections at Edinburgh University, said the letter written in Burke's blood was found by accident in a scrapbook which had collated contemporary material about the murders, such as songs, poems and reports of the trial.

He said: "The university has a very rich historical department of anatomy and we have been doing quite a lot more work with that collection recently - this is one of the things that came to light in the process.

"When we picked it up it was a little scrapbook which didn't look that exciting in the first instance.

"But when we opened up, it is basically a collection of stuff which was being sold on the street about the trails and the execution - and a letter claiming to be written in Burke's own blood.

"After he was hanged, they obviously took something as a souvenir - it is almost like a medieval relic."

Marshall said the colour of the writing suggested it was genuine blood, but there were no clues to the identity of the author.

The letter will be on display as part of the 'One Last Fright' weekend, being held by the University of Edinburgh over 15-17 May. A series of free events, which are ticketed, aim to reveal the most sinister stories from the university's vast archives, which includes historic material in special collections stretching 35 kilometres and 400,000 rare books.

A petition drawn up by students at Edinburgh University in 1828 demanding more bodies to practice anatomy on, will also be on display. It was recently bought by the university from a private collection.

Marshall said: "It has presumably been in private hands since the early 19th century. It is about six feet long and signed by a couple of hundred students at the university.

"I think because the Burke and Hare murders were discovered so soon afterwards, the students were probably really embarrassed about having signed this petition.

"So it has been hidden away ever since and it is only now someone has gone through an attic or something it has been discovered."

The brutal crimes of William Burke and William Hare, who prowled the streets of Edinburgh and killed victims to sell their bodies to the university's medical school, both shocked and fascinated the nation.

At the time of the murders, the only legal source of corpses which could be used for anatomy training was executed murderers. But fewer executions taking place and an increasing demand for bodies to train medical students led to an rise in the illegal practice of body-snatching - digging up corpses from graves to sell to anatomists.

However Burke and Hare took it a step further by killing at least 16 people in 1828 to sell their corpses to Professor Robert Knox, a leading anatomist at Edinburgh University.

Burke was hanged for his crimes and publicly dissected - and his skeleton is still held in the university's anatomy museum. Hare escaped the hangman's noose by agreeing to testify against his accomplice.

Marshall said the enduring fascination with the Burke and Hare murders fitted with the 'Jekyll and Hyde' image of Edinburgh.

"It is the idea that on one level you have got these very respectable doctors giving lectures to wealthy students and it is all very correct and nice - but underneath that, in a tunnel, there are literally murdered bodies being dragged in," he said.

"To many people it is the image they have of Edinburgh - all very nice and correct on the outside, but when you dig a little deeper it is dark down there."