When you enter into the Library of the Raccoon City Police Department for the first time you are going to see that there’s a puzzle within the rows of books in the area that you’re going to need to solve to reach portions of the third floor of the building that will ultimately let you reach the Clock Tower.
On the main floor of the library there are four three moveable bookshelves and one that has a jack underneath of it. To release this jack you are going to need to recover the Jack’s handle. This item is located in the Records Room in the Police Department.
The Records Room is located in the west side of the Police Department on the first floor (1F). To access the Records Room you will need to have gotten the Club Key in Leon’s play through which can only be found in the Boiler Room taped to a whiteboard.
Once you have the handle to the jack you can remove the jack from under the bookshelf. You will then need to move the shelves to form a bridge above where the broken walkway is. You will then move the bookshelves into position and cross over to the third floor main hall area.
Once you have access to the third floor via the Library you can access the Clock Tower which will allow you to pick up one of the electrical pieces to solve the jail cell door puzzle, you can access the third floor of the main hall and unlock a door that connects the third floors of the East and West sides of the building.