Continuity mistake: When Sara is waiting with Greg for the results for what was inside the tyre that exploded, she grabs the paper straight off the printer, reads it, looks at Greg and takes off immediately to inform Gil. When Grissom looks at the paper, you can see Greg's name is signed at the bottom as confirmation, but he never got anywhere near the paper.
Continuity mistake: The Camaro at the crash scene is a late second generation model (built from 1970 - 1981), however in the flashbacks to the crash it's a third generation car (82 - 92). The difference in body styles is quite pronounced.
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.