Complex sentence: Lambert of Hersfeld reports that during the night, driven by bodily needs, he went to the toilet and a gunman who was lurking the stuck a sword between the buttocks leaving the weapon planted in the wound.
Split into simpler sentences: Lambert of Hersfeld reports that during the night, driven by bodily needs, he went to the toilet. An assassin who was lurking there stuck a sword between the buttocks leaving the weapon planted in the wound.