Complex sentence: Realising that only a full confession will absolve him, yet fearing the consequences, he decides to kill the last vestige of his conscience--for it is conscience that has brought him to where he stands now.
Split into simpler sentences: Realising that only a full confession will absolve him, yet fearing the consequences, he decides to kill the last vestige of his conscience. For it is conscience that has brought him to where he stands now.