You will need to get to the 3rd floor and there is a window on the left hand side.

Smash the bottom two glass sections and repair the window so two planks will appear you will have to jump on the left hand side of the window.

Then when you get to the top of the window planks you will have to jump + crouch so you get on top of the window frame, then you will have to jump + crouch again so you are on little ledge that you can see through.
Note, you can not shoot through the ledge. You will not be able to pick up any of the special power ups unless you jump down.

You will be able to get the achivement Hands of Merchandise, but unless someone jumps down the thief will not be able to find you.