During chapter 3, when you sneak in the building there should be the guards desk with one magazine, to get the next one you must turn to your left and walk straight toward the adjoining hallway
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After this youll find a set of double doors on the left. Open them and head through the next hallway until you reach a blue door. Open it and go down the stairs.
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Youll enter a circular hallway (this is also where youll find the alarm system, if youd like to shut it off). Head around to the far side, where youll find this solitary door:

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Go inside and walk to your left. Youll see the next issue laying in there.

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