I'm going to rule that Sam's position within the church hierarchy gives hir a pretty good idea of who's in jail at any given time, (assuming they've been in jail at least 6 hours) after about 30 seconds going over the church records.  (knowing who committed what crimes is, after all, very important for a number of church ministries, such as the Last Meals of Arwai, the Independent Investigators of Aureon, the Bounty Hunters of Balinor, the Arbitrators of Boldrei, the Barristers of Kol Korran, and the Wardens of  Onatar; so they collect full records on all publically available criminal cases)