I have gotten Tirdir out of his grave in the graveyard and spoken with the grave digger and he gave me a red patch of cloak to find the culprit which is somewhere in the bridge district I have looked everywhere in the bridge district with no luck of finding a match for the red piece of cloth or any clues

I'm also trying to resuce Haer' Dalis from the Wizard Mekrath my journal says Mekrath's hideout can be accessed from the sewers the only sewer I know of is where I got Lilarcor and snuck into the slavers hideout and I have looked everywhere down there and nothing. Sorry for the long post

Spoilers
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I found the red cloak guy near the doorto the most south westernbuilding on the bridge map. I am unsure if you need to actually do something to make him appear though.

Check the sewers in the temple district. You may need to stop at the temple of him first to access them. There are a few entrances there though. There is one in front of the "guarded compound"

SPOILERS
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1. Am-si (the guy who put Tirdir in the grave) can be found in the Bridge District in the SW corner between 2 buildings right on the edge of the bridge.

2. Mekrath - go to the temple district. If you have not already done so, speak to the guy at the Temple of Helm about the 'Unseeing Eye' cult, this will enable you to get into the sewers (rescuing Haer'Dalis is not the only quest stemming from these sewers). There are 2 secret doors on the most northern wall of the sewers, the western one is the one you want.

Thank you!