There is the report.

Armand Waters

The events are as follows --

A man, strapped with explosives, wandered into the Chapterhouse. I [Armand Waters] asked him what he was doing, and he ranted some nonsense about his devil-master. He seemed to have some difficulty engaging the explosives. I had sufficient time to keep well away from the blast, and to remove various papers and books of importance. After a moment's time he blew himself up and started a large fire on the Chapterhouse Zurkhplank flooring. With the able assistance of many adventurers, the fire was extinguished.

Armand

The cult worships an entity called Ithikraszt, and often makes references to a "dakr flame". Their official apparel seems to be a blood red armor and a mask with a skull's visage. Wesley is the only confirmed cultist.

The grounds are, obviously, a concealed attack on a sanctioned building in upper Santuary with intent to kill and damage.

Lathander's light, Helm watch over this,

-- Laramie [A simple stylized drawing of an open eye]