Today's Observer has a fascinating article regarding the faces of two of Scotland's most infamous murderers. 180 years after their brutal crimes a rare pair of plaster masks Burke and Hare have been found at Inveraray jail in Argyll, along with a genuine hangman's noose. This discovery is strange in that neither of the murderers was ever held at Inveraray, nor was anyone ever hanged inside the prison.

"We found the masks during a clean-out of one of our store rooms, it was quite a surprise," said Gavin Dick, the general manager of the jail, which is now a museum. "Initially we thought it was just Burke, but it turns out we've got two heads. A death mask of Burke and a life mask of Hare. Unfortunately very little is known about either head, or for that matter the hangman's noose, and how they came to be here."

William Burke and William Hare are among the most notorious of Scotland's criminals whosupplied bodies for dissection to the anatomist Robert Knox in Edinburgh. However, instead of robbing graves, the pair found it easier to kill rather than exhume their victims.

Until the 1832 Anatomy Act, the only legal sources of corpses for anatomical purposes in the UK were those of people condemned to death and dissection by the courts. However as the need to train medical students increased, the number of executed criminals fell, so Knox was only too glad to receive the Irishmen's wares. It is believed that Burke and Hare murdered at least 16 people, possibly as many as 30, before their crimes were discovered. Hare turned King's evidence and escaped the gallows, while Burke was publicly executed and his body exhibited before being flayed and dissected. A number of ghoulish souvenirs were kept of Burke, including a book and a snuff box bound in pieces of his skin. His skeleton is still kept under lock and key at Edinburgh University.

The activities of the former navvies, who had originally moved to Edinburgh to work on the Union Canal, repelled and fascinated the public. A life mask is known to have been made of Hare during the trial, and Burke's shaven head was cast after his execution in front of 25,000 people on 28 January 1829. Although a handful of masks are known to still exist, with at least one in the United States, one in a museum in Swansea and copies at the universities of St Andrews and Edinburgh, they are very rare. "How or why they should end up in Inveraray jail is a something of a mystery," said Owen Dudley Edwards, the author of several works about the murderous pair. "There are no links at all between Inveraray and Burke and Hare, so it seems a very unlikely place to find these masks. There have been cases where copies have shown up in strange places, usually because they were once owned by private collectors, but there certainly weren't many of them made.

Although there was much public anger at the fact that Hare was allowed to go free, attempts to bring further charges against him failed and he fled to England. The man described at the time as a "rude ruffian, ferocious profligate" and "evidently the greatest villain of the two" was last seen heading east from Carlisle on the road to Newcastle. There were reports that he was living at Buckminster in Leicestershire until his identity was discovered and he was forced to move on. He is said to have died a blind beggar in London, or even emigrated to the US.

Andrew Connell, museum collections manager at the Royal College of Surgeons, which has its own copy of Burke's death mask, said the find was definitely unusual: "I've not seen them anywhere else. I don't think they were like Charles and Diana souvenirs. There was probably only a handful made, if that."

Staff at Inveraray jail are considering whether to exhibit the masks and the noose alongside their existing house of horrors, such as a cat o' nine tails, and a tongue holder for nagging wives, which are used to illustrate the history of crime and punishment in Scotland.