With the use of psionic powers our agents have already discovered something important.
Apparently the cultist has a complete copy of the Teonomicon is his house! This is an extremely important document. It must be retrieved as quickly as possible before his allies remove all the evidence. His home is located in the Astral Quarter. Go there and find this book.
Also look for a certain knife. We're not sure why it's important, but the prisoner is constantly thinking about it. It might be used in important rituals.