He was found to have recently injected a concoction related to "Demonic Blood," and his "Scar of Blaze Tooth" had disappeared without a trace.
Of course, everyone knew he had been framed, because there was simply no reason for him to do so.
But since he chose not to call his family at the time, he could not prove his innocence. Since the result of soul-searching could not be shown to a third party, it could not serve as evidence... However, his use of Demonic Blood could indeed be used as evidence.
For the Roaring Fang family, who strongly emphasize leaving no "loose ends," this essentially cut off his path to ascent.
It was also because of the clear awareness that someone seemed to be targeting the "Roaring Fang" family... that those who had tried to murder Arthur when he was young refrained from laying hands on him during his misfortune.
