Complex sentence: He was discovered by The Rev. Andrew Knox, a Protestant minister (who later became both Lord Bishop of the Isles and Lord Bishop of Raphoe), and thereafter either tried to escape or deliberately drowned himself in the sea off Ailsa Craig.
Split into simpler sentences: He was discovered by The Rev. Andrew Knox, a Protestant minister (who later became both Lord Bishop of the Isles and Lord Bishop of Raphoe). Barclay thereafter either tried to escape or deliberately drowned himself in the sea off Ailsa Craig.