On this page of our guide to BioShock Infinite you will find the second part of a detailed walkthrough of Chapter 22 - Bull House Impound. Leave the building after obtaining the gunsmith's tools. Also, you can find a new voxophone.
After you have located the gunsmith's tools and passed through a tear made by Elizabeth, return to the police station. Make sure to check a room near the entrance to the cellar, because there's a Voxophone #47 on the desk.
Proceed to the yard located in front of the police impound. Leave the building to advance to the next level.