Why is Detective Parsons leery of investigating Bob Sullivan in the novel, All Is Not Forgotten?

Parsons does not want to investigate Bob Sullivan because he is afraid of all the lawsuits that will be filed. When Sullivan's alibi does not check out, however, Parsons is stuck with investigating the town's richest, most powerful man. When Bob's wife shares his real alibi with Parsons, the detective is disgusted to learn the details of his affair with the young secretary.