Service of All the Dead — Colin Dexter

CHURCHWARDEN MURDERED DURING SERVICE
... screamed the headlines. But Inspector Morse found there was more to it than the headlines. Two bodies more, for a start.

After the second death, the case was closed. Everyone agreed the murderer had committed suicide.

Everyone but Morse. He sensed the unrest that still fermented in the Oxford parish. He found new evidence and new discrepancies. He also found an attractive lady by the name of Ruth Rawlinson.

And then they found another body...