
Continuity mistake: When Sara is showing Greg the route the old woman took in her car, she draws a blue line on the screen with her finger. When she says something about turning left she draws a continuous line to the "Meadows Lane," but when the shot changes and goes back the line is broken into two.
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.