Complex sentence: Although all the witnesses, including Zouche, agreed that the gamekeeper's death was a tragic accident, Abbot's reputation never recovered from the fact that he was the only Archbishop of Canterbury ever to kill a man.
Split into simpler sentences: Although all the witnesses, including Zouche, agreed that the gamekeeper's death was a tragic accident, Abbot's reputation never recovered from the incident. He was the only Archbishop of Canterbury ever to kill a man.