Turn to the left and look for eyes on the wall. She'll open up a new door for you at the top of the staircase you came up before. Break the lock with the Sledgehammer and slide the ladder down to the far end of the room.
Since your flashlight is busted, wait for Rosa to bring some light down.
Now that you have a Crowbar, backtrack to the beginning of the level. When you're ready, look for a staircase and go up it. Look on the receptionist's desk to find a dead bird. Some of the shelves will be knocked over allowing you to go through a new passage. The villain is waiting for you on the other side, but he quickly hops into the elevator. Once they are gone, you'll have to find weapons on your own. Approach it slowly and then fire a shot at his head when he pops out to attack.
View all the Achievements here Find guides to this achievement here. Since you're not much for acrobatics, look for another way up. After the cut scene, you'll be instructed to follow Detective Dickenson to a crime scene. When you've got the info you need from the microfiche, get out of the library.
