In book 1, Bigger accidentally killed Mary Dalton by suffocating her when bringing her home one night. After he kills her, he decides to burn her body to hide the evidence, but has to cut her head off to fit her in the furnace but has two "burning pools" of accusation and guilt while doing it showing the fear he is feeling. This fear is reflected throughout book 1 because Bigger feels trapped and this causes him to be violent and act in rash manners.
In book 2, Bigger is home the morning after he killed Mary and is with his family having breakfast. Buddy asks him about his job and at first he is nervous talking but calms down and thinks that the murder was natural and "not once did he feel the need to tell himself that it had been an accident." This shows that he no longer feels this fear and is empowered and broke the racial barrier and can never go back by killing Mary.
In book 3, after being caught after killing Mary, Bigger comes to terms with who he is and feels fine about being a killer. This statement shows that he accepted his fate and is willing to die if it must be. Max seems very startled about this comment and tells Bigger that he isn't a monster but Bigger believes he was fated to be a killer.