It was the contract.
Kyanite led everyone to the room where the Disciplinary Committee kept their contracts, and sure enough, the contract protecting Arc's identity had been turned to ashes. As the "Holder" of the contract, Kyan had suffered the most from its destruction, though Raven wasn't far behind as a result of some particular quality of her blood magic that Veng didn't share. The teachers quickly confirmed that all signatories experienced some degree of pain simultaneously.
Much of what was discussed over the hours-long investigation went right over Arc's head, but it soon became clear there wasn't enough evidence to bring any particular suspect forward, especially because the Disciplinary Committee's room had been locked the moment Kyan left, and there were no signs of entry.
And of course, Arc dreaded the moment the rest of the family found out, an inevitability with Cory and Sylvia involved.
