This set of quests is driving me crazy. All the thieves in the sewer and in the cave are long since dead. At one time, I had both letters in my possession but in talking to someone (maybe Marcus; maybe Tingalf, I can't remember) the letter from Victorio to Pedro disappeared. Since then, talking to Marcus gets me "Anything new??" talking to the Lieutenant of Guards gets me "Yes, we know all about Tingalf....." and talking to Tingalf gets me "I have a secret cache but won't tell you." Obviously, I've done something (or a lot of things) out of order, but is there any way to resolve this mess?