Complex sentence: Clark did not claim to have been one of the executioners, but he wrote about the killings without apology, believing them to be justifiable revenge for murdered Kentucky settlers and a means to intimidate Indians into stopping their raids.
Split into simpler sentences: Clark did not claim to have been one of the executioners. He later wrote about the killings without apology, believing them to be justifiable revenge for murdered Kentucky settlers and a means to intimidate Indians into stopping their raids.