Revealing mistake: When Grissom finds Isabelle Millander dead in her chair, you can see her blink as the shot changes, even though she's supposed to be dead.
Continuity mistake: Supposedly, Paul Millander was 10 years old when his father was killed. A newspaper report read by Sara in 1x08(Time 39:45) says this. It also says that his father died August 17th, 1959. In 2x13(Time 43:18), in the last scene, Grissom looks at Paul's birth certificate. It says that Paul was born August 17th, 1956, which would mean that he was actually 3 years old when his father died. (00:39:45 - 00:43:15)
Revealing mistake: After Grissom finds Isabelle Millander dead in her chair, he walks towards the bathroom. When the shot changes, you can see her shift her legs even though she's supposed to be dead.
Answer: He doesn't have the authority to arrest him - when anyone is arrested in the show, a police officer does it. Also he tells Ty that he is going to be submitting his case findings to Ty's insurance company, who would no doubt contact the IRS, who then would have him arrested for fraud etc.