After you finish the Salamandra outpost in the sewers, you should see our old friend Jailer Jethro waiting for you right outside. Talk to him, and he'll direct you to another section of the sewers, where the head of the operation is; that person is the one who has the documents in question.And in the swamps, freeing the three groups of enslaved brickmakers doesn't give you the documents. AFTER those groups have all been freed, talk to Vaska and to the Hierophant in the Druid's Grove. The Hierophant will help you lure the biggest bad guy in the swamps to a place where he (AND his tame wyvern) will help you kill the guy. The other document you need is on that guy's corpse, once you kill him.