How does the reader learn how Dawn would be murdered?

The reader learns about how Dawn would be murdered when Westbrook asks Boggs why OJ Simpson would choose a knife as a murder weapon over a gun with a silencer. Boggs response is that a knife is the most phallic of murder weapons, and "if you want to fuck your babe to death, you use a knife. You stick it in all the way." This makes it very clear to the reader what is to come next.