The police are knee-jerk anti-gun nuts.
This is obviously an old, historically valuable weapon that has probably been in that book since the original owner died and his heirs were unaware of what it was.
It belongs in a display case, not in a police department locker.
My uncle used to have a pair of black powder, muzzle loading dueling pistols in the drawer of his library, along with loading rod, a few patches, and some lead balls. Those things are really cool, not something for the police to confiscate and mistreat.
This gun is a cheap replica. Somebody cut out a book and put a magnetic cabinet clasp on it to make a display piece. It’s actual value is about $50, including the book.