One of the missing notebooks contains Charles Darwin's iconic 1837 "Tree of Life" sketch. After a thorough search, however, the library has concluded that the notebooks were likely stolen.
"I am heartbroken that the location of these Darwin notebooks, including Darwin's iconic "Tree of Life" drawing, is now unknown, but we're determined to do everything possible to discover what happened and will leave no stone unturned during this process", Jessica Gardner, university librarian and director of library services since 2017, said in a statement.
The handwritten documents first outlining early notions of evolution were last seen in at the University in 2000, when an external request was made to photograph Darwin's work.
British police are now investigating and Interpol has been notified.More news: Houthi attack on Saudi Aramco plant damages oil tank
As for why it took so long for the library to report the notebooks missing: Though a number of searches had turned up nothing as to their whereabouts, the prevailing assumption among Gardner's predecessors was that the notebooks simply had been "misfiled", the librarian told the BBC. "Now if anything of this scale and significance was not found, we would be going to the police", she said.
Dr Gardner reported the matter to police.
She said there are now no leads. The town celebrates him with a Darwin Festival, and there is a statue of him outside the town centre library where he went to school.
Staff recently searched through 189 boxes making up the Darwin Archive, but failed to locate the notebooks.
Dr Gardner said that security policy was different 20 years ago, adding: "Today any such significant missing object would be reported as a potential theft immediately and a widespread search begun".More news: Google brings 'The Mandalorian' to AR in its new app
She added: "We've devoted the whole of our careers to the preservation of cultural heritage and we're devastated by what has happened".
Professor Stephen J Toope, vice-chancellor of the university, said: "Cambridge University Library is one of the world's great libraries and home to globally important collections, assembled and cared for over six centuries, and encompassing thousands of years of human thought and discovery".
The little drawing, better known among scholars as the "Tree of Life" sketch, reveals elements of Darwin's thinking more than two decades before he fleshed out his ideas in his ground-breaking On the Origin of Species.
The library first lost track of the notebooks in 2001, after they were taken out of the Special Collections Strong Rooms to clear room for a photography project to be carried out there.More news: China opposes Indian govt ban of its mobile apps