As you make your way through the Tower following the meeting with Brecken and Jade you see a bloke hanging out in a doorway in the hall named Dawud - he wants you to find him a gun. Specifically a pistol.
This is one weapon you will not find as loot on Bandits or infected. The only way that we know of to obtain one is either to grab the one on the floor in the hut in the corner of The Slums, or to find one in the Police Vehicles (Vans) whose locks you pick.
Either way once you have one you return to him and complete the mission - which then gives you access to the Pawn Shop.
After you hand over the gun and he gives you the keys to the shop, he asks you for an additional favor - he wants you to obtain a Roy McCall Action Figure from the shop for his son.
You may not know this but that is an Easter Egg Homage to Call of Juarez - that being a character from that game! Not surprisingly Techland also worked on that game.
You will find the following collectibles in the Pawn Shop:
Note #06
Note #07
You will also find a bunch of resources for crafting as well!
Okay - you know that old saying No Good Deed Goes Unpunished? Yeah well... The man takes the pistol you gave him and uses it to take his kid with him - leaving his wife behind - to flee the Tower!
Now you have to maybe sort of try to make this right?