”It was assumed at the time that this was an isolated incident.”

Scotland’s national archive has traced the mysterious disappearance of more than 3,000 historical documents over a period of 30 years to a history professor with an all-consuming interest in stamps. The theft began to unravel when a National Records of Scotland archivist attended an auction in London in 1994. There, he discovered that 200 of the items for sale belonged to the archive, some still marked with their NRS reference numbers.

Whoops! So, no stocktaking is ever carried out? 

The items, 3,100 items in total, mainly family, estate and business correspondence, were traced back to an academic and archivist, Prof David Macmillan, who died in 1987. Records showed that he made annual visits to the NRS archives as a user from 1969 until 1980, when he was caught taking a single item from the archive in Edinburgh and his access was immediately revoked. It was assumed at the time that this was an isolated incident.

/facepalm. 

That's like catching a mouse in your kitchen, letting it go in the garden and saying 'job done!' and never thinking 'Maybe there could be more than one?' 

But the scale of his thefts became apparent in 2012, when a researcher saw a reference in an online catalogue at Trent University to an item he thought may have belonged in Scotland and raised concerns. NRS archivists went on to discover about 2,900 items which had been stolen by Macmillan and then gifted to Trent University’s archives after his death.

Good grief, you couldn't make it up, could you? 

The correspondence he took was not of high financial or historical value, and it remains a mystery why someone whose own working life was sustained by the use of archives would abuse the trust of these institutions in such a blatant manner.

People do all sorts of strange things for all sorts of reasons. Sensible organisations prepare for this by having security measures. It would appear the National Archive of Scotland is not such an organisation. 

NRS now has almost all its documents back in their rightful position, overseen by more robust security measures than Macmillan encountered, which protect its collection of 38m documents spanning nearly 1,000 years of Scottish history.

Congratulations, you've now shut the stable door after the unicorn has galloped over the banks and braes with the loot!