Warehouse Keeper Mia:
We need at least 10 pieces of the key and 1 Records Chest in order to find open it and find the evidence our client has asked for.
Go to the Field of Silence and get rid of the Tasaba Lizardmen and Tasaba Lizardman Shaman there. Once you have done so, you will be able to obtain both the pieces of the key to the Records Chest and the Records Chest itself.