Continuity mistake: A prostitute is questioned in the interrogation room. Her teeth are stained brown. In one shot, most of her teeth are stained. In the next, one her front teeth is perfectly white and the others are brown.
Continuity mistake: Morgan and Finn are walking and talking about a case. Morgan has a folder in her hand. The folder is visibly closed. She looks down and shows Finn a case file. The shot shows a case file with photo and text on an open folder. Next shot shows the folder closed again.
Continuity mistake: When Sam the police dog picks up a bottle of water with his mouth from a cooler, he picks it up from the top. In the next frame, he gives it to his trainer horizontally.
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.