Continuity mistake: When Catherine tells Grisson she liked the tough act (while listening to the guy testify) he said too much, she said not enough. Then he glances over at her. The guy is talking, which indicates a continuous line, even though the shot changes, but Grissom is not looking at Catherine during the shot change, instead he's got his head leaning against the glass.
Continuity mistake: When Brown talks to David, David pulls out a pelvis from a vat of acid, saying he's cleaning it. In one shot the pelvis is hanging off the lower of the tongs, but in the next shot it's clamped between the tongs. This series of shots occurs a couple times during the conversation.
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.