Brother Griswald was a Hammerite. He could be found behind the clock tower on day 3 in Thief: Deadly Shadows.
Brother Griswald was worried about Inspector Drept and talked to Brother Mendon on the subject. He wasn't impressed the he did not do the Builders work but searched The City for information on the grey lady, as well as using the title 'Inspector' instead of Brother, and was known to be helping and working with Garrett.[1]