What event has made rev. hale uneasy about the court's proceedings?

In Act III, Reverend Hale denounces the proceedings of the court because he believes the testimony of John Proctor. "But it does not follow that everyone accused is a part of it." "I have evidence for the court." "...private vengeance is working through this testimony." "Is every defense an attack upon the court?" private vengeance is working through this testimony.