I'd love to hire him Though he'd probably show up a few times at my door!

With the caveat that it's from the 70s and theres no computers or mobile/cell phones going around it's still pretty accurate and interesting and it reads like the author knew libraries fairly well. I can't find much about him (in the few minutes of googling all I could find was the French Wikipedia listing) but he seems to have been a prolific short-story writer. These were pretty slight and quick stories without too much depth but as a story of a retired police detective trying to live the quiet life as a tracker-down of missing and overdue library books it was entertaining and right up my alley.

Because he's an ex-cop he gets himself interested in the lives of the people he's interacting with and once he gets a sniff that there's something off it's hard to stop him, today he would probably get reprimanded for using too much of his time to solve these mysteries and would probably be suffering under a quota load.

In several of the stories he interacts with a Lieutenant Randall who has his own series.

Library Fuzz (1972) - opens with a dead body where Hal Johnson is just trying to find an overdue book.
More Than a Mere Storybook (1973) - Hal almost gets knocked out when in a house and finds more than just missing library books.
The Bookmark (1973) - when he retrieves books his car is broken into, what's in one of the books leads to solving a mystery.
The Elusive Mrs. Stout (1974) - an elusive borrower promises to be there when Hal arrives but things get complicated.
Still a Cop (1975) - a library book is linked to a murder.
The Mutilated Scholar (1976) - Hal recognises a library book on the bus as being a book stolen when his car was stolen and solving this mystery is complicated.
The Savanarola Syndrome - many copies of a book are going missing and this investigation is going to lead to potentially explosive finale.

There are apparently 3 more stories in this series (they don't list the Savanarola Syndrome on wikipedia and it may have had another name in other markets) but there are apparently 3 more stories to hunt down:
The Young Runners (1978)
The Reward (1980)
The Book Clue (1984)
I'd like to read more by this author, I enjoyed the reads and while slight they are decent enough. ( )