I don't think so Vinny will look for the black box in a bookshelf. He will be looking for a book. The only question is what kind of book he is looking for. I think so that in this respect there are two possibilities.
Possibility 1:
The MC thought once with himself, when he clicked the diary of his mother, when it lay alone in the bookshelf, so that he should put it in the safe. In fact, he later put it in the side cabinet of his bed. But Vinny wanted to get into the safe first before going through the MC's bookshelf. Therefore, I think so Vinny was looking for Lynette's diary. Why? There will be a secret in the diary that he doesn't want the MC to know.
Possibility 2:
What if Rusty has created a kind of "Book of the President" where also all DIK secrets including the reasons of each DIK secret code are written down and passed from DIK president to DIK president. Such a book would be worth its weight in gold for whoever wants to harm the DIKs. It doesn't matter if Vinny wants to harm the DIKs or is working with someone who wants to harm the DIKs. Such a book should be put in a safe or hidden in a library among many other books. But Vinny knows about the former library and is looking for it there.