Never heard about this before. Anyway I've checked on the Net, and while it's true that there have been rumors about the isle being haunted by the supposed ghosts of plague victims, in fact nowhere it is spoken about remarkable events, still less splatter details. In my opinion this account is much exaggerated and imaginative.
It seems that until some years ago it has been a favourite place of practitioners of black masses, since the place was abandoned. Now however it's going to be opened to tourism.
You may be interested in this
website.