Living Doll - S7-E24
Revealing mistake: Grissom and Brass enter the darkened apt. and Grissom spots another doll figurine on the book shelf as Brass takes notice of the dead guy on the bathroom floor. As Grissom comments on this being yet another 'miniature killer' scene, the cam flips to a shot of Dead Guy and he wiggles just slightly, even though he'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.