A literary vandal is stalking the streets of Herne Bay in Kent, ripping pages in half in dozens of books in a charity shop and library before replacing them on shelves.

Ryan Campbell, the chief executive of the charity Demelza, which runs a bookshop on Mortimer Street, told the Guardian that since April, around 100 books in the shop have had their pages torn in half horizontally before being reshelved.

“We think it’s been going on for a few months but it’s hard to tell – if you find a ripped book in a secondhand shop you don’t think too much about it, so it’s taken us a while to piece it together. But whatever this person has been doing has been escalating,” said Campbell. “I’m trying not to be too Sherlock Holmes about it, but if there’s such a thing as a quite distinctive rip, well, he or she rips the page in half horizontally and sometimes removes half the page.”

Campbell said that the damage has been stepped up over the last few weeks to “quite a few” copies a week, estimating that this has cost the charity, which provides care for children with serious and terminal conditions, several hundred pounds.

“Of course people donate these books towards the care of children with terminal illness so it’s almost like taking the collection box,” he said.

The culprit, who has been dubbed the “book ripper”, targets books out of sight of the till – particularly in the true crime section.

Although signs have been put up to try to stop the vandal, and the police have been alerted, as yet there are no leads. Herne Bay library told the Herne Bay Gazette that it had also had books damaged over the last six months, with members of staff “now being extra-watchful to try to catch the person responsible or at least cut down on the opportunities to cause more damage”, according to a council spokesperson.

Campbell said: “We’ve had to brief our staff that if you find someone doing it then don’t apprehend them. The library has got CCTV and there’s no trace of who’s doing it. But at some point this will either stop – or if it doesn’t then at some point this person will be caught.”

Campbell, who is also the former chair of mental health charity Mind, expressed his concerns about the psychology of the book ripper. “This is very systematic; it’s quite an anonymous, private thing to do, and it’s not the action of a happy person. So it makes you think a little bit about who’s doing this and why they feel the need to do it and what’s going on in their lives,” he said. “I’ve got images of vigilantes prowling the local bookshops and libraries waiting to pounce on whoever’s doing this, and although I’d really like it to stop and someone to be caught, I’m a little bit worried about the person.”