The Vampire Trial
The interrogation process had begun, and there was no need for the vampires to use thier influence powers on Fex. Due to Fex unique position and the strange circumstances, he was first kept in confinement at the castle to be watched over and then would be moved at a later time. This was because the others still did not know that Fex had actually snuck out instead. Instead, they stuck with the story of Fex having being ordered. If they had known the truth, they would have never allowed this as an option.
While in confinement, there were several guards, not just of the Sanguinis family, but also of the other families. They would stay just outside of his room at all times, making sure he didn't escape.