From the county archivist:
Those against whom a bill of indictment (that is, a formal criminal charge) had been made were first placed before a grand jury, whose function was to hear evidence for the Crown. If it was decided that there was a case to be answered by the accused, the indictment was declared to be a ‘true bill’ (billa vera); if not it was ‘no bill’ (ignoramus)[meaning we do not know]. In the former case, the accused then went forward to a full trial. The grand jury procedure was abolished in 1933.