What revelation during the investigation leads to Bob Sullivan's murder in the novel, All Is Not Forgotten?

Using the power of suggestion, Forrester imprints the idea in Jenny's mind that Bob could be the rapist. A quick background check turns up an old charge filed against him during college when he had consensual sex with a minor. The alibi Bob gave police did not check out, which makes him look even more like a suspect in Jenny's rape. In trying to clear her husband's name, Fran Sullivan, gives police details that prove he was with a young woman at the time of Jenny's rape. The young woman is the daughter of his friend and his secretary at one of the dealerships. When the young woman's father learns of their sexual relationship, he beats Bob to death with a crowbar at the car dealership.