I'll be honest. I never liked the Mysterious Killings quest. The premise is solid, but the actual execution and rewards aren't believable. The idea of the Office of the Watch will willingly give you the sacred armour of a fallen Ordinator all seems half-assed to me. This mod intends to make the quest more worthwhile.
This mod replaces the old Indoril helm and cuirass that was offered as a reward for the quest with a new set. I never understood why a pious Ordinator like Elam Andas would willingly hand over a set of armour the he acknowledges as being sacred, so the armour is now replaced with a new set that is considered a personal gift from Elam.
There is also now a small camp that spawns along with the Dreamer Prophet that contains some Sixth House memrobilia that will be siezed by the Order of the Watch once you've reported your success to Elam.
Future plans include making the quest time sensitive, with the murderer killing more Ordinators if you aren't quick in stopping them, or even for the Order of the Watch to do their job and catch the killer before you do. Other plans include having the killer in a random location, requiring more shrewd rumour chasing and detective work.
The mod overhauls the entire quest and makes some minor changes to the Foreign Quarter waterworks, but it should be compatible with whatever Vivec overhaul you have installed (hopefully).