The Grim Reaper by Bernard Knight
Sixth novel in the increasingly popular mediaeval mystery series featuring Crowner John, Devon's first county coroner. May 1195, and Sir John de Wolfe is faced with a strange series of serial murders, which begins with the suffocation of a Jewish money-lender and proceeds through that of a London harlot, a dissolute priest and a burgess suspected of abusing young boys. The common factor is that an appropriate Biblical text is left at each murder scene, the mode of which reflects the alleged sin of the victim. This means that a literate and Bible-learned killer is involved - which, in an age where only 1% of the population can read or write - can only be a priest. There are seventeen parish churches in Exeter, so the killer could be any one of about a hundred clerics. Crowner John sets about to discover the identity of the homicidal priest.