LONDON — Two of naturalist Charles Darwin’s notebooks that were reported stolen from Cambridge University have been returned, two decades after they disappeared.

The university said Tuesday that the manuscripts were left in its library inside a pink gift bag, along with a note wishing the librarian a Happy Easter.

The notebooks were wrapped tightly in cling wrap.

The notebooks went missing in 2001, though at the time staff believed they might have been misplaced.

After searches failed to find them, they were reported stolen to police in October 2020. On March 9, the books reappeared, left in a public area of the building, outside the librarian’s office.

It’s not known who may have returned them, as there were no surveillance cameras in that area.

Police are now reviewing surveillance video from other areas of the building.

Library officials had to get permission from police to take the notebooks out of the wrapping to examine them.

The notebooks include the 19th-century scientist’s famous “Tree of Life” sketch and are valued at millions of dollars.

They will now be kept in a secure strongroom at the library and go on display this summer.