Mithras is annoyed at the news that Azariah Thelas escaped using teleportation, but asks you to search his house just in case there's some clue to his destination.
If you head back to the house and have a quick look around, you should quickly find a trapdoor that was previously covered up. Head through this and you will be in a small room filled with crates of ebony. There is also another trap door that seems to lead into an underground tunnel system. Activate this door to receive a journal update.
The following Journal ID and Index codes can be used with the Journalconsole command to manually update the quest to a certain point.
The Final Search (TR_m1_RR_MQ_9)
Index
Finishes Quest
Journal Entry
10
Mithras told me to search Azariah Thelas' house, to see if there might be any clues as to his location.
20
In Azariah's hidden basement, I found a trapdoor that appeared to lead into some kind of underground tunnel system. I should inform Mithras immediately, before I explore any further.
30
Finishes quest
Mithras was shocked to hear about the tunnel in Azariah's house. He is sure that it must lead into the city's ancient catacombs, which Mithras had sealed shut many years ago.