A candidate. Some supporter of a candidate, who left his patroness unaware. The Venatori, to sow more confusion and anger in the Chantry. An old, private enemy of Agathe's. A group of madmen, with goals only they know.

I do not really think the candidates themselves are likely- but we cannot know, unless an investigation is conducted. And if one is chosen who is involved, would she not have the power to bury the evidence?