Regillus

REgillus was a member of Aqua Sulis, until he was corrupted by a demon and eventually confessed to diabolism.

Regillus was corrupted by a demon he thought was the ghost of a Roman soldier. The ghost tricked him into using infernal Vis in his Longevity Ritual.
Then the ghost threatened to turn him in to the Order of Hermes if he didn't help the ghost spy on other Magi the ghost thought corruptible.
He did as the ghost bid for several years, but spent most of that time studying to escape the creatures clutches.
He learned enough Rego Vim to create a ward that would keep the demon out of his sanctum, and began living in it.
His sodales became concerned and notified the Quaesitors, after which Regillus confessed to his crimes, and begged for mercy.
The tribunal, in an effort to encourage diabolists to turn themselves in, granted him leniency.
Regillus is under house arrest for the rest of his life, in an Aegis which he has no token for.