He sought to become one of the Chosen and became furious when he was rejected. Determined to achieve immortality, in his rage, he destroyed the building and incorporated his spirit into the place.
Clues led Tom, Rainer, and Drirr to the Argim's place. They found a Trii-like structure, which Drirr made contact with. The structure turned out to be Argim's consciousness. Argim moved itself away to allow the party reaching the murderer's remains, in turn he asks them to bring him a music crystal, which can be bought from Wania.
If anyone else than Drirr attempts to touch Argim, he gets shocked, and the party gets an option to attact the structure. After the structure is defeated, the whole place dies with it, too.