Sacred Haven of Debauchery

Resurrecting corpses is certainly unethical, but it does present a certain theoretical interest. And as for his crimes, Hawke put it very well: "It wasn't the mage who killed people, it was a madman. He could have done the same with a knife."

Orsino himself says that he helped Quentin. You can ask the Temple guards about the mages, briefly, before the transformation, and you can even ask the Temple knights about this.
As for the madness, an ordinary person won't suddenly become obsessed, only with the help of a mage, but a mage...

Besides, he was red in the inventory!

Yes, I just looked for screenshots.

Added after 35 seconds

Another reason to leave this position and do something simpler.

Probably, she would have done just that, leaving the position to Callen. But it didn't work out, because of the idol.