Character mistake: When Catherine slams the trash can lid shut outside and heads to the car to answer her phone, she tells her Mum 'Catherine threw something out', referring to Lindsay.
Revealing mistake: Willows discloses a laptop with the city's grid layout inside the welder's truck, and grabs her cell to call Grissom. Just as she presses last number, he immediately answers, without so much even a ring.
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.