Continuity mistake: When Grisson gets on the vibrating bed, in the close up shots he is sitting with his neck even to the top of the headboard and no pillow showing. In the wide-angle shot, he's hunched down lower with a lot of the pillow showing above his shoulders.
Revealing mistake: The outline of dead Ice Guys underwear can be seen at the very bottom of the screen when Catherine and Nick take a DNA sample from his ear.
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.